linux/arch/x86/kernel/kvmclock.c
Marcelo Tosatti 7539b174ae x86: kvmguest: use TSC clocksource if invariant TSC is exposed
The invariant TSC bit has the following meaning:

"The time stamp counter in newer processors may support an enhancement,
referred to as invariant TSC. Processor's support for invariant TSC
is indicated by CPUID.80000007H:EDX[8]. The invariant TSC will run
at a constant rate in all ACPI P-, C-. and T-states. This is the
architectural behavior moving forward. On processors with invariant TSC
support, the OS may use the TSC for wall clock timer services (instead
of ACPI or HPET timers). TSC reads are much more efficient and do not
incur the overhead associated with a ring transition or access to a
platform resource."

IOW, TSC does not change frequency. In such case, and with
TSC scaling hardware available to handle migration, it is possible
to use the TSC clocksource directly, whose system calls are
faster.

Reduce the rating of kvmclock clocksource to allow TSC clocksource
to be the default if invariant TSC is exposed.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

v2: Use feature bits and tsc_unstable() check (Sean Christopherson)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2019-02-20 22:48:52 +01:00

371 lines
9.4 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/* KVM paravirtual clock driver. A clocksource implementation
Copyright (C) 2008 Glauber de Oliveira Costa, Red Hat Inc.
*/
#include <linux/clocksource.h>
#include <linux/kvm_para.h>
#include <asm/pvclock.h>
#include <asm/msr.h>
#include <asm/apic.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/cpuhotplug.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/set_memory.h>
#include <asm/hypervisor.h>
#include <asm/mem_encrypt.h>
#include <asm/x86_init.h>
#include <asm/reboot.h>
#include <asm/kvmclock.h>
static int kvmclock __initdata = 1;
static int kvmclock_vsyscall __initdata = 1;
static int msr_kvm_system_time __ro_after_init = MSR_KVM_SYSTEM_TIME;
static int msr_kvm_wall_clock __ro_after_init = MSR_KVM_WALL_CLOCK;
static u64 kvm_sched_clock_offset __ro_after_init;
static int __init parse_no_kvmclock(char *arg)
{
kvmclock = 0;
return 0;
}
early_param("no-kvmclock", parse_no_kvmclock);
static int __init parse_no_kvmclock_vsyscall(char *arg)
{
kvmclock_vsyscall = 0;
return 0;
}
early_param("no-kvmclock-vsyscall", parse_no_kvmclock_vsyscall);
/* Aligned to page sizes to match whats mapped via vsyscalls to userspace */
#define HV_CLOCK_SIZE (sizeof(struct pvclock_vsyscall_time_info) * NR_CPUS)
#define HVC_BOOT_ARRAY_SIZE \
(PAGE_SIZE / sizeof(struct pvclock_vsyscall_time_info))
static struct pvclock_vsyscall_time_info
hv_clock_boot[HVC_BOOT_ARRAY_SIZE] __bss_decrypted __aligned(PAGE_SIZE);
static struct pvclock_wall_clock wall_clock __bss_decrypted;
static DEFINE_PER_CPU(struct pvclock_vsyscall_time_info *, hv_clock_per_cpu);
static struct pvclock_vsyscall_time_info *hvclock_mem;
static inline struct pvclock_vcpu_time_info *this_cpu_pvti(void)
{
return &this_cpu_read(hv_clock_per_cpu)->pvti;
}
static inline struct pvclock_vsyscall_time_info *this_cpu_hvclock(void)
{
return this_cpu_read(hv_clock_per_cpu);
}
/*
* The wallclock is the time of day when we booted. Since then, some time may
* have elapsed since the hypervisor wrote the data. So we try to account for
* that with system time
*/
static void kvm_get_wallclock(struct timespec64 *now)
{
wrmsrl(msr_kvm_wall_clock, slow_virt_to_phys(&wall_clock));
preempt_disable();
pvclock_read_wallclock(&wall_clock, this_cpu_pvti(), now);
preempt_enable();
}
static int kvm_set_wallclock(const struct timespec64 *now)
{
return -ENODEV;
}
static u64 kvm_clock_read(void)
{
u64 ret;
preempt_disable_notrace();
ret = pvclock_clocksource_read(this_cpu_pvti());
preempt_enable_notrace();
return ret;
}
static u64 kvm_clock_get_cycles(struct clocksource *cs)
{
return kvm_clock_read();
}
static u64 kvm_sched_clock_read(void)
{
return kvm_clock_read() - kvm_sched_clock_offset;
}
static inline void kvm_sched_clock_init(bool stable)
{
if (!stable)
clear_sched_clock_stable();
kvm_sched_clock_offset = kvm_clock_read();
pv_ops.time.sched_clock = kvm_sched_clock_read;
pr_info("kvm-clock: using sched offset of %llu cycles",
kvm_sched_clock_offset);
BUILD_BUG_ON(sizeof(kvm_sched_clock_offset) >
sizeof(((struct pvclock_vcpu_time_info *)NULL)->system_time));
}
/*
* If we don't do that, there is the possibility that the guest
* will calibrate under heavy load - thus, getting a lower lpj -
* and execute the delays themselves without load. This is wrong,
* because no delay loop can finish beforehand.
* Any heuristics is subject to fail, because ultimately, a large
* poll of guests can be running and trouble each other. So we preset
* lpj here
*/
static unsigned long kvm_get_tsc_khz(void)
{
setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
return pvclock_tsc_khz(this_cpu_pvti());
}
static void __init kvm_get_preset_lpj(void)
{
unsigned long khz;
u64 lpj;
khz = kvm_get_tsc_khz();
lpj = ((u64)khz * 1000);
do_div(lpj, HZ);
preset_lpj = lpj;
}
bool kvm_check_and_clear_guest_paused(void)
{
struct pvclock_vsyscall_time_info *src = this_cpu_hvclock();
bool ret = false;
if (!src)
return ret;
if ((src->pvti.flags & PVCLOCK_GUEST_STOPPED) != 0) {
src->pvti.flags &= ~PVCLOCK_GUEST_STOPPED;
pvclock_touch_watchdogs();
ret = true;
}
return ret;
}
struct clocksource kvm_clock = {
.name = "kvm-clock",
.read = kvm_clock_get_cycles,
.rating = 400,
.mask = CLOCKSOURCE_MASK(64),
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
EXPORT_SYMBOL_GPL(kvm_clock);
static void kvm_register_clock(char *txt)
{
struct pvclock_vsyscall_time_info *src = this_cpu_hvclock();
u64 pa;
if (!src)
return;
pa = slow_virt_to_phys(&src->pvti) | 0x01ULL;
wrmsrl(msr_kvm_system_time, pa);
pr_info("kvm-clock: cpu %d, msr %llx, %s", smp_processor_id(), pa, txt);
}
static void kvm_save_sched_clock_state(void)
{
}
static void kvm_restore_sched_clock_state(void)
{
kvm_register_clock("primary cpu clock, resume");
}
#ifdef CONFIG_X86_LOCAL_APIC
static void kvm_setup_secondary_clock(void)
{
kvm_register_clock("secondary cpu clock");
}
#endif
/*
* After the clock is registered, the host will keep writing to the
* registered memory location. If the guest happens to shutdown, this memory
* won't be valid. In cases like kexec, in which you install a new kernel, this
* means a random memory location will be kept being written. So before any
* kind of shutdown from our side, we unregister the clock by writing anything
* that does not have the 'enable' bit set in the msr
*/
#ifdef CONFIG_KEXEC_CORE
static void kvm_crash_shutdown(struct pt_regs *regs)
{
native_write_msr(msr_kvm_system_time, 0, 0);
kvm_disable_steal_time();
native_machine_crash_shutdown(regs);
}
#endif
static void kvm_shutdown(void)
{
native_write_msr(msr_kvm_system_time, 0, 0);
kvm_disable_steal_time();
native_machine_shutdown();
}
static void __init kvmclock_init_mem(void)
{
unsigned long ncpus;
unsigned int order;
struct page *p;
int r;
if (HVC_BOOT_ARRAY_SIZE >= num_possible_cpus())
return;
ncpus = num_possible_cpus() - HVC_BOOT_ARRAY_SIZE;
order = get_order(ncpus * sizeof(*hvclock_mem));
p = alloc_pages(GFP_KERNEL, order);
if (!p) {
pr_warn("%s: failed to alloc %d pages", __func__, (1U << order));
return;
}
hvclock_mem = page_address(p);
/*
* hvclock is shared between the guest and the hypervisor, must
* be mapped decrypted.
*/
if (sev_active()) {
r = set_memory_decrypted((unsigned long) hvclock_mem,
1UL << order);
if (r) {
__free_pages(p, order);
hvclock_mem = NULL;
pr_warn("kvmclock: set_memory_decrypted() failed. Disabling\n");
return;
}
}
memset(hvclock_mem, 0, PAGE_SIZE << order);
}
static int __init kvm_setup_vsyscall_timeinfo(void)
{
#ifdef CONFIG_X86_64
u8 flags;
if (!per_cpu(hv_clock_per_cpu, 0) || !kvmclock_vsyscall)
return 0;
flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
if (!(flags & PVCLOCK_TSC_STABLE_BIT))
return 0;
kvm_clock.archdata.vclock_mode = VCLOCK_PVCLOCK;
#endif
kvmclock_init_mem();
return 0;
}
early_initcall(kvm_setup_vsyscall_timeinfo);
static int kvmclock_setup_percpu(unsigned int cpu)
{
struct pvclock_vsyscall_time_info *p = per_cpu(hv_clock_per_cpu, cpu);
/*
* The per cpu area setup replicates CPU0 data to all cpu
* pointers. So carefully check. CPU0 has been set up in init
* already.
*/
if (!cpu || (p && p != per_cpu(hv_clock_per_cpu, 0)))
return 0;
/* Use the static page for the first CPUs, allocate otherwise */
if (cpu < HVC_BOOT_ARRAY_SIZE)
p = &hv_clock_boot[cpu];
else if (hvclock_mem)
p = hvclock_mem + cpu - HVC_BOOT_ARRAY_SIZE;
else
return -ENOMEM;
per_cpu(hv_clock_per_cpu, cpu) = p;
return p ? 0 : -ENOMEM;
}
void __init kvmclock_init(void)
{
u8 flags;
if (!kvm_para_available() || !kvmclock)
return;
if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
} else if (!kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
return;
}
if (cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "kvmclock:setup_percpu",
kvmclock_setup_percpu, NULL) < 0) {
return;
}
pr_info("kvm-clock: Using msrs %x and %x",
msr_kvm_system_time, msr_kvm_wall_clock);
this_cpu_write(hv_clock_per_cpu, &hv_clock_boot[0]);
kvm_register_clock("primary cpu clock");
pvclock_set_pvti_cpu0_va(hv_clock_boot);
if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);
x86_platform.calibrate_tsc = kvm_get_tsc_khz;
x86_platform.calibrate_cpu = kvm_get_tsc_khz;
x86_platform.get_wallclock = kvm_get_wallclock;
x86_platform.set_wallclock = kvm_set_wallclock;
#ifdef CONFIG_X86_LOCAL_APIC
x86_cpuinit.early_percpu_clock_init = kvm_setup_secondary_clock;
#endif
x86_platform.save_sched_clock_state = kvm_save_sched_clock_state;
x86_platform.restore_sched_clock_state = kvm_restore_sched_clock_state;
machine_ops.shutdown = kvm_shutdown;
#ifdef CONFIG_KEXEC_CORE
machine_ops.crash_shutdown = kvm_crash_shutdown;
#endif
kvm_get_preset_lpj();
/*
* X86_FEATURE_NONSTOP_TSC is TSC runs at constant rate
* with P/T states and does not stop in deep C-states.
*
* Invariant TSC exposed by host means kvmclock is not necessary:
* can use TSC as clocksource.
*
*/
if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
!check_tsc_unstable())
kvm_clock.rating = 299;
clocksource_register_hz(&kvm_clock, NSEC_PER_SEC);
pv_info.name = "KVM";
}