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![Linus Torvalds](/assets/img/avatar_default.png)
- The biggest change is the rework of the percpu code, to support the 'Named Address Spaces' GCC feature, by Uros Bizjak: - This allows C code to access GS and FS segment relative memory via variables declared with such attributes, which allows the compiler to better optimize those accesses than the previous inline assembly code. - The series also includes a number of micro-optimizations for various percpu access methods, plus a number of cleanups of %gs accesses in assembly code. - These changes have been exposed to linux-next testing for the last ~5 months, with no known regressions in this area. - Fix/clean up __switch_to()'s broken but accidentally working handling of FPU switching - which also generates better code. - Propagate more RIP-relative addressing in assembly code, to generate slightly better code. - Rework the CPU mitigations Kconfig space to be less idiosyncratic, to make it easier for distros to follow & maintain these options. - Rework the x86 idle code to cure RCU violations and to clean up the logic. - Clean up the vDSO Makefile logic. - Misc cleanups and fixes. [ Please note that there's a higher number of merge commits in this branch (three) than is usual in x86 topic trees. This happened due to the long testing lifecycle of the percpu changes that involved 3 merge windows, which generated a longer history and various interactions with other core x86 changes that we felt better about to carry in a single branch. ] Signed-off-by: Ingo Molnar <mingo@kernel.org> -----BEGIN PGP SIGNATURE----- iQJFBAABCgAvFiEEBpT5eoXrXCwVQwEKEnMQ0APhK1gFAmXvB0gRHG1pbmdvQGtl cm5lbC5vcmcACgkQEnMQ0APhK1jUqRAAqnEQPiabF5acQlHrwviX+cjSobDlqtH5 9q2AQy9qaEHapzD0XMOxvFye6XIvehGOGxSPvk6CoviSxBND8rb56lvnsEZuLeBV Bo5QSIL2x42Zrvo11iPHwgXZfTIusU90sBuKDRFkYBAxY3HK2naMDZe8MAsYCUE9 nwgHF8DDc/NYiSOXV8kosWoWpNIkoK/STyH5bvTQZMqZcwyZ49AIeP1jGZb/prbC e/rbnlrq5Eu6brpM7xo9kELO0Vhd34urV14KrrIpdkmUKytW2KIsyvW8D6fqgDBj NSaQLLcz0pCXbhF+8Nqvdh/1coR4L7Ymt08P1rfEjCsQgb/2WnSAGUQuC5JoGzaj ngkbFcZllIbD9gNzMQ1n4Aw5TiO+l9zxCqPC/r58Uuvstr+K9QKlwnp2+B3Q73Ft rojIJ04NJL6lCHdDgwAjTTks+TD2PT/eBWsDfJ/1pnUWttmv9IjMpnXD5sbHxoiU 2RGGKnYbxXczYdq/ALYDWM6JXpfnJZcXL3jJi0IDcCSsb92xRvTANYFHnTfyzGfw EHkhbF4e4Vy9f6QOkSP3CvW5H26BmZS9DKG0J9Il5R3u2lKdfbb5vmtUmVTqHmAD Ulo5cWZjEznlWCAYSI/aIidmBsp9OAEvYd+X7Z5SBIgTfSqV7VWHGt0BfA1heiVv F/mednG0gGc= =3v4F -----END PGP SIGNATURE----- Merge tag 'x86-core-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull core x86 updates from Ingo Molnar: - The biggest change is the rework of the percpu code, to support the 'Named Address Spaces' GCC feature, by Uros Bizjak: - This allows C code to access GS and FS segment relative memory via variables declared with such attributes, which allows the compiler to better optimize those accesses than the previous inline assembly code. - The series also includes a number of micro-optimizations for various percpu access methods, plus a number of cleanups of %gs accesses in assembly code. - These changes have been exposed to linux-next testing for the last ~5 months, with no known regressions in this area. - Fix/clean up __switch_to()'s broken but accidentally working handling of FPU switching - which also generates better code - Propagate more RIP-relative addressing in assembly code, to generate slightly better code - Rework the CPU mitigations Kconfig space to be less idiosyncratic, to make it easier for distros to follow & maintain these options - Rework the x86 idle code to cure RCU violations and to clean up the logic - Clean up the vDSO Makefile logic - Misc cleanups and fixes * tag 'x86-core-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (52 commits) x86/idle: Select idle routine only once x86/idle: Let prefer_mwait_c1_over_halt() return bool x86/idle: Cleanup idle_setup() x86/idle: Clean up idle selection x86/idle: Sanitize X86_BUG_AMD_E400 handling sched/idle: Conditionally handle tick broadcast in default_idle_call() x86: Increase brk randomness entropy for 64-bit systems x86/vdso: Move vDSO to mmap region x86/vdso/kbuild: Group non-standard build attributes and primary object file rules together x86/vdso: Fix rethunk patching for vdso-image-{32,64}.o x86/retpoline: Ensure default return thunk isn't used at runtime x86/vdso: Use CONFIG_COMPAT_32 to specify vdso32 x86/vdso: Use $(addprefix ) instead of $(foreach ) x86/vdso: Simplify obj-y addition x86/vdso: Consolidate targets and clean-files x86/bugs: Rename CONFIG_RETHUNK => CONFIG_MITIGATION_RETHUNK x86/bugs: Rename CONFIG_CPU_SRSO => CONFIG_MITIGATION_SRSO x86/bugs: Rename CONFIG_CPU_IBRS_ENTRY => CONFIG_MITIGATION_IBRS_ENTRY x86/bugs: Rename CONFIG_CPU_UNRET_ENTRY => CONFIG_MITIGATION_UNRET_ENTRY x86/bugs: Rename CONFIG_SLS => CONFIG_MITIGATION_SLS ...
554 lines
14 KiB
C
554 lines
14 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Generic entry points for the idle threads and
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* implementation of the idle task scheduling class.
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*
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* (NOTE: these are not related to SCHED_IDLE batch scheduled
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* tasks which are handled in sched/fair.c )
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*/
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/* Linker adds these: start and end of __cpuidle functions */
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extern char __cpuidle_text_start[], __cpuidle_text_end[];
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/**
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* sched_idle_set_state - Record idle state for the current CPU.
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* @idle_state: State to record.
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*/
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void sched_idle_set_state(struct cpuidle_state *idle_state)
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{
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idle_set_state(this_rq(), idle_state);
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}
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static int __read_mostly cpu_idle_force_poll;
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void cpu_idle_poll_ctrl(bool enable)
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{
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if (enable) {
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cpu_idle_force_poll++;
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} else {
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cpu_idle_force_poll--;
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WARN_ON_ONCE(cpu_idle_force_poll < 0);
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}
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}
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#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
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static int __init cpu_idle_poll_setup(char *__unused)
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{
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cpu_idle_force_poll = 1;
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return 1;
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}
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__setup("nohlt", cpu_idle_poll_setup);
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static int __init cpu_idle_nopoll_setup(char *__unused)
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{
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cpu_idle_force_poll = 0;
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return 1;
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}
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__setup("hlt", cpu_idle_nopoll_setup);
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#endif
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static noinline int __cpuidle cpu_idle_poll(void)
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{
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instrumentation_begin();
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trace_cpu_idle(0, smp_processor_id());
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stop_critical_timings();
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ct_cpuidle_enter();
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raw_local_irq_enable();
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while (!tif_need_resched() &&
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(cpu_idle_force_poll || tick_check_broadcast_expired()))
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cpu_relax();
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raw_local_irq_disable();
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ct_cpuidle_exit();
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start_critical_timings();
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trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
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local_irq_enable();
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instrumentation_end();
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return 1;
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}
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/* Weak implementations for optional arch specific functions */
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void __weak arch_cpu_idle_prepare(void) { }
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void __weak arch_cpu_idle_enter(void) { }
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void __weak arch_cpu_idle_exit(void) { }
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void __weak __noreturn arch_cpu_idle_dead(void) { while (1); }
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void __weak arch_cpu_idle(void)
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{
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cpu_idle_force_poll = 1;
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}
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#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST_IDLE
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DEFINE_STATIC_KEY_FALSE(arch_needs_tick_broadcast);
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static inline void cond_tick_broadcast_enter(void)
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{
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if (static_branch_unlikely(&arch_needs_tick_broadcast))
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tick_broadcast_enter();
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}
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static inline void cond_tick_broadcast_exit(void)
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{
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if (static_branch_unlikely(&arch_needs_tick_broadcast))
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tick_broadcast_exit();
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}
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#else
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static inline void cond_tick_broadcast_enter(void) { }
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static inline void cond_tick_broadcast_exit(void) { }
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#endif
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/**
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* default_idle_call - Default CPU idle routine.
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*
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* To use when the cpuidle framework cannot be used.
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*/
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void __cpuidle default_idle_call(void)
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{
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instrumentation_begin();
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if (!current_clr_polling_and_test()) {
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cond_tick_broadcast_enter();
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trace_cpu_idle(1, smp_processor_id());
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stop_critical_timings();
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ct_cpuidle_enter();
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arch_cpu_idle();
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ct_cpuidle_exit();
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start_critical_timings();
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trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
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cond_tick_broadcast_exit();
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}
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local_irq_enable();
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instrumentation_end();
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}
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static int call_cpuidle_s2idle(struct cpuidle_driver *drv,
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struct cpuidle_device *dev)
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{
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if (current_clr_polling_and_test())
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return -EBUSY;
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return cpuidle_enter_s2idle(drv, dev);
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}
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static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
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int next_state)
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{
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/*
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* The idle task must be scheduled, it is pointless to go to idle, just
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* update no idle residency and return.
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*/
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if (current_clr_polling_and_test()) {
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dev->last_residency_ns = 0;
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local_irq_enable();
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return -EBUSY;
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}
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/*
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* Enter the idle state previously returned by the governor decision.
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* This function will block until an interrupt occurs and will take
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* care of re-enabling the local interrupts
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*/
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return cpuidle_enter(drv, dev, next_state);
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}
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/**
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* cpuidle_idle_call - the main idle function
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*
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* NOTE: no locks or semaphores should be used here
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*
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* On architectures that support TIF_POLLING_NRFLAG, is called with polling
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* set, and it returns with polling set. If it ever stops polling, it
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* must clear the polling bit.
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*/
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static void cpuidle_idle_call(void)
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{
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struct cpuidle_device *dev = cpuidle_get_device();
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struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
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int next_state, entered_state;
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/*
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* Check if the idle task must be rescheduled. If it is the
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* case, exit the function after re-enabling the local irq.
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*/
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if (need_resched()) {
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local_irq_enable();
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return;
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}
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/*
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* The RCU framework needs to be told that we are entering an idle
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* section, so no more rcu read side critical sections and one more
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* step to the grace period
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*/
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if (cpuidle_not_available(drv, dev)) {
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tick_nohz_idle_stop_tick();
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default_idle_call();
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goto exit_idle;
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}
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/*
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* Suspend-to-idle ("s2idle") is a system state in which all user space
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* has been frozen, all I/O devices have been suspended and the only
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* activity happens here and in interrupts (if any). In that case bypass
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* the cpuidle governor and go straight for the deepest idle state
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* available. Possibly also suspend the local tick and the entire
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* timekeeping to prevent timer interrupts from kicking us out of idle
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* until a proper wakeup interrupt happens.
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*/
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if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) {
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u64 max_latency_ns;
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if (idle_should_enter_s2idle()) {
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entered_state = call_cpuidle_s2idle(drv, dev);
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if (entered_state > 0)
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goto exit_idle;
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max_latency_ns = U64_MAX;
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} else {
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max_latency_ns = dev->forced_idle_latency_limit_ns;
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}
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tick_nohz_idle_stop_tick();
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next_state = cpuidle_find_deepest_state(drv, dev, max_latency_ns);
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call_cpuidle(drv, dev, next_state);
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} else {
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bool stop_tick = true;
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/*
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* Ask the cpuidle framework to choose a convenient idle state.
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*/
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next_state = cpuidle_select(drv, dev, &stop_tick);
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if (stop_tick || tick_nohz_tick_stopped())
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tick_nohz_idle_stop_tick();
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else
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tick_nohz_idle_retain_tick();
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entered_state = call_cpuidle(drv, dev, next_state);
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/*
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* Give the governor an opportunity to reflect on the outcome
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*/
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cpuidle_reflect(dev, entered_state);
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}
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exit_idle:
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__current_set_polling();
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/*
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* It is up to the idle functions to reenable local interrupts
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*/
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if (WARN_ON_ONCE(irqs_disabled()))
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local_irq_enable();
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}
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/*
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* Generic idle loop implementation
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*
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* Called with polling cleared.
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*/
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static void do_idle(void)
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{
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int cpu = smp_processor_id();
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/*
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* Check if we need to update blocked load
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*/
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nohz_run_idle_balance(cpu);
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/*
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* If the arch has a polling bit, we maintain an invariant:
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*
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* Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
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* rq->idle). This means that, if rq->idle has the polling bit set,
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* then setting need_resched is guaranteed to cause the CPU to
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* reschedule.
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*/
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__current_set_polling();
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tick_nohz_idle_enter();
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while (!need_resched()) {
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rmb();
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/*
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* Interrupts shouldn't be re-enabled from that point on until
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* the CPU sleeping instruction is reached. Otherwise an interrupt
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* may fire and queue a timer that would be ignored until the CPU
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* wakes from the sleeping instruction. And testing need_resched()
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* doesn't tell about pending needed timer reprogram.
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*
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* Several cases to consider:
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*
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* - SLEEP-UNTIL-PENDING-INTERRUPT based instructions such as
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* "wfi" or "mwait" are fine because they can be entered with
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* interrupt disabled.
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*
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* - sti;mwait() couple is fine because the interrupts are
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* re-enabled only upon the execution of mwait, leaving no gap
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* in-between.
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*
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* - ROLLBACK based idle handlers with the sleeping instruction
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* called with interrupts enabled are NOT fine. In this scheme
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* when the interrupt detects it has interrupted an idle handler,
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* it rolls back to its beginning which performs the
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* need_resched() check before re-executing the sleeping
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* instruction. This can leak a pending needed timer reprogram.
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* If such a scheme is really mandatory due to the lack of an
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* appropriate CPU sleeping instruction, then a FAST-FORWARD
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* must instead be applied: when the interrupt detects it has
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* interrupted an idle handler, it must resume to the end of
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* this idle handler so that the generic idle loop is iterated
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* again to reprogram the tick.
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*/
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local_irq_disable();
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if (cpu_is_offline(cpu)) {
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cpuhp_report_idle_dead();
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arch_cpu_idle_dead();
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}
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arch_cpu_idle_enter();
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rcu_nocb_flush_deferred_wakeup();
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/*
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* In poll mode we reenable interrupts and spin. Also if we
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* detected in the wakeup from idle path that the tick
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* broadcast device expired for us, we don't want to go deep
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* idle as we know that the IPI is going to arrive right away.
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*/
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if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
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tick_nohz_idle_restart_tick();
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cpu_idle_poll();
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} else {
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cpuidle_idle_call();
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}
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arch_cpu_idle_exit();
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}
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/*
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* Since we fell out of the loop above, we know TIF_NEED_RESCHED must
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* be set, propagate it into PREEMPT_NEED_RESCHED.
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*
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* This is required because for polling idle loops we will not have had
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* an IPI to fold the state for us.
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*/
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preempt_set_need_resched();
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tick_nohz_idle_exit();
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__current_clr_polling();
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/*
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* We promise to call sched_ttwu_pending() and reschedule if
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* need_resched() is set while polling is set. That means that clearing
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* polling needs to be visible before doing these things.
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*/
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smp_mb__after_atomic();
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/*
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* RCU relies on this call to be done outside of an RCU read-side
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* critical section.
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*/
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flush_smp_call_function_queue();
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schedule_idle();
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if (unlikely(klp_patch_pending(current)))
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klp_update_patch_state(current);
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}
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bool cpu_in_idle(unsigned long pc)
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{
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return pc >= (unsigned long)__cpuidle_text_start &&
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pc < (unsigned long)__cpuidle_text_end;
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}
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struct idle_timer {
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struct hrtimer timer;
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int done;
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};
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static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
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{
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struct idle_timer *it = container_of(timer, struct idle_timer, timer);
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WRITE_ONCE(it->done, 1);
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set_tsk_need_resched(current);
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return HRTIMER_NORESTART;
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}
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void play_idle_precise(u64 duration_ns, u64 latency_ns)
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{
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struct idle_timer it;
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/*
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* Only FIFO tasks can disable the tick since they don't need the forced
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* preemption.
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*/
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WARN_ON_ONCE(current->policy != SCHED_FIFO);
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WARN_ON_ONCE(current->nr_cpus_allowed != 1);
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WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
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WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
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WARN_ON_ONCE(!duration_ns);
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WARN_ON_ONCE(current->mm);
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rcu_sleep_check();
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preempt_disable();
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current->flags |= PF_IDLE;
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cpuidle_use_deepest_state(latency_ns);
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it.done = 0;
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hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
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it.timer.function = idle_inject_timer_fn;
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hrtimer_start(&it.timer, ns_to_ktime(duration_ns),
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HRTIMER_MODE_REL_PINNED_HARD);
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while (!READ_ONCE(it.done))
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do_idle();
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cpuidle_use_deepest_state(0);
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current->flags &= ~PF_IDLE;
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preempt_fold_need_resched();
|
|
preempt_enable();
|
|
}
|
|
EXPORT_SYMBOL_GPL(play_idle_precise);
|
|
|
|
void cpu_startup_entry(enum cpuhp_state state)
|
|
{
|
|
current->flags |= PF_IDLE;
|
|
arch_cpu_idle_prepare();
|
|
cpuhp_online_idle(state);
|
|
while (1)
|
|
do_idle();
|
|
}
|
|
|
|
/*
|
|
* idle-task scheduling class.
|
|
*/
|
|
|
|
#ifdef CONFIG_SMP
|
|
static int
|
|
select_task_rq_idle(struct task_struct *p, int cpu, int flags)
|
|
{
|
|
return task_cpu(p); /* IDLE tasks as never migrated */
|
|
}
|
|
|
|
static int
|
|
balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
|
|
{
|
|
return WARN_ON_ONCE(1);
|
|
}
|
|
#endif
|
|
|
|
/*
|
|
* Idle tasks are unconditionally rescheduled:
|
|
*/
|
|
static void wakeup_preempt_idle(struct rq *rq, struct task_struct *p, int flags)
|
|
{
|
|
resched_curr(rq);
|
|
}
|
|
|
|
static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
|
|
{
|
|
}
|
|
|
|
static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
|
|
{
|
|
update_idle_core(rq);
|
|
schedstat_inc(rq->sched_goidle);
|
|
}
|
|
|
|
#ifdef CONFIG_SMP
|
|
static struct task_struct *pick_task_idle(struct rq *rq)
|
|
{
|
|
return rq->idle;
|
|
}
|
|
#endif
|
|
|
|
struct task_struct *pick_next_task_idle(struct rq *rq)
|
|
{
|
|
struct task_struct *next = rq->idle;
|
|
|
|
set_next_task_idle(rq, next, true);
|
|
|
|
return next;
|
|
}
|
|
|
|
/*
|
|
* It is not legal to sleep in the idle task - print a warning
|
|
* message if some code attempts to do it:
|
|
*/
|
|
static void
|
|
dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
|
|
{
|
|
raw_spin_rq_unlock_irq(rq);
|
|
printk(KERN_ERR "bad: scheduling from the idle thread!\n");
|
|
dump_stack();
|
|
raw_spin_rq_lock_irq(rq);
|
|
}
|
|
|
|
/*
|
|
* scheduler tick hitting a task of our scheduling class.
|
|
*
|
|
* NOTE: This function can be called remotely by the tick offload that
|
|
* goes along full dynticks. Therefore no local assumption can be made
|
|
* and everything must be accessed through the @rq and @curr passed in
|
|
* parameters.
|
|
*/
|
|
static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
|
|
{
|
|
}
|
|
|
|
static void switched_to_idle(struct rq *rq, struct task_struct *p)
|
|
{
|
|
BUG();
|
|
}
|
|
|
|
static void
|
|
prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
|
|
{
|
|
BUG();
|
|
}
|
|
|
|
static void update_curr_idle(struct rq *rq)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Simple, special scheduling class for the per-CPU idle tasks:
|
|
*/
|
|
DEFINE_SCHED_CLASS(idle) = {
|
|
|
|
/* no enqueue/yield_task for idle tasks */
|
|
|
|
/* dequeue is not valid, we print a debug message there: */
|
|
.dequeue_task = dequeue_task_idle,
|
|
|
|
.wakeup_preempt = wakeup_preempt_idle,
|
|
|
|
.pick_next_task = pick_next_task_idle,
|
|
.put_prev_task = put_prev_task_idle,
|
|
.set_next_task = set_next_task_idle,
|
|
|
|
#ifdef CONFIG_SMP
|
|
.balance = balance_idle,
|
|
.pick_task = pick_task_idle,
|
|
.select_task_rq = select_task_rq_idle,
|
|
.set_cpus_allowed = set_cpus_allowed_common,
|
|
#endif
|
|
|
|
.task_tick = task_tick_idle,
|
|
|
|
.prio_changed = prio_changed_idle,
|
|
.switched_to = switched_to_idle,
|
|
.update_curr = update_curr_idle,
|
|
};
|