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https://github.com/torvalds/linux
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2b4f3b4987
Patch series "Avoid memory corruption caused by per-VMA locks", v4.
A memory corruption was reported in [1] with bisection pointing to the
patch [2] enabling per-VMA locks for x86. Based on the reproducer
provided in [1] we suspect this is caused by the lack of VMA locking while
forking a child process.
Patch 1/2 in the series implements proper VMA locking during fork. I
tested the fix locally using the reproducer and was unable to reproduce
the memory corruption problem.
This fix can potentially regress some fork-heavy workloads. Kernel build
time did not show noticeable regression on a 56-core machine while a
stress test mapping 10000 VMAs and forking 5000 times in a tight loop
shows ~7% regression. If such fork time regression is unacceptable,
disabling CONFIG_PER_VMA_LOCK should restore its performance. Further
optimizations are possible if this regression proves to be problematic.
Patch 2/2 disables per-VMA locks until the fix is tested and verified.
This patch (of 2):
When forking a child process, parent write-protects an anonymous page and
COW-shares it with the child being forked using copy_present_pte().
Parent's TLB is flushed right before we drop the parent's mmap_lock in
dup_mmap(). If we get a write-fault before that TLB flush in the parent,
and we end up replacing that anonymous page in the parent process in
do_wp_page() (because, COW-shared with the child), this might lead to some
stale writable TLB entries targeting the wrong (old) page. Similar issue
happened in the past with userfaultfd (see flush_tlb_page() call inside
do_wp_page()).
Lock VMAs of the parent process when forking a child, which prevents
concurrent page faults during fork operation and avoids this issue. This
fix can potentially regress some fork-heavy workloads. Kernel build time
did not show noticeable regression on a 56-core machine while a stress
test mapping 10000 VMAs and forking 5000 times in a tight loop shows ~7%
regression. If such fork time regression is unacceptable, disabling
CONFIG_PER_VMA_LOCK should restore its performance. Further optimizations
are possible if this regression proves to be problematic.
Link: https://lkml.kernel.org/r/20230706011400.2949242-1-surenb@google.com
Link: https://lkml.kernel.org/r/20230706011400.2949242-2-surenb@google.com
Fixes:
|
||
|---|---|---|
| .. | ||
| bpf | ||
| cgroup | ||
| configs | ||
| debug | ||
| dma | ||
| entry | ||
| events | ||
| futex | ||
| gcov | ||
| irq | ||
| kcsan | ||
| livepatch | ||
| locking | ||
| module | ||
| power | ||
| printk | ||
| rcu | ||
| sched | ||
| time | ||
| trace | ||
| .gitignore | ||
| acct.c | ||
| async.c | ||
| audit.c | ||
| audit.h | ||
| audit_fsnotify.c | ||
| audit_tree.c | ||
| audit_watch.c | ||
| auditfilter.c | ||
| auditsc.c | ||
| backtracetest.c | ||
| bounds.c | ||
| capability.c | ||
| cfi.c | ||
| compat.c | ||
| configs.c | ||
| context_tracking.c | ||
| cpu.c | ||
| cpu_pm.c | ||
| crash_core.c | ||
| crash_dump.c | ||
| cred.c | ||
| delayacct.c | ||
| dma.c | ||
| exec_domain.c | ||
| exit.c | ||
| extable.c | ||
| fail_function.c | ||
| fork.c | ||
| freezer.c | ||
| gen_kheaders.sh | ||
| groups.c | ||
| hung_task.c | ||
| iomem.c | ||
| irq_work.c | ||
| jump_label.c | ||
| kallsyms.c | ||
| kallsyms_internal.h | ||
| kallsyms_selftest.c | ||
| kallsyms_selftest.h | ||
| kcmp.c | ||
| Kconfig.freezer | ||
| Kconfig.hz | ||
| Kconfig.locks | ||
| Kconfig.preempt | ||
| kcov.c | ||
| kexec.c | ||
| kexec_core.c | ||
| kexec_elf.c | ||
| kexec_file.c | ||
| kexec_internal.h | ||
| kheaders.c | ||
| kprobes.c | ||
| ksyms_common.c | ||
| ksysfs.c | ||
| kthread.c | ||
| latencytop.c | ||
| Makefile | ||
| module_signature.c | ||
| notifier.c | ||
| nsproxy.c | ||
| padata.c | ||
| panic.c | ||
| params.c | ||
| pid.c | ||
| pid_namespace.c | ||
| pid_sysctl.h | ||
| profile.c | ||
| ptrace.c | ||
| range.c | ||
| reboot.c | ||
| regset.c | ||
| relay.c | ||
| resource.c | ||
| resource_kunit.c | ||
| rseq.c | ||
| scftorture.c | ||
| scs.c | ||
| seccomp.c | ||
| signal.c | ||
| smp.c | ||
| smpboot.c | ||
| smpboot.h | ||
| softirq.c | ||
| stackleak.c | ||
| stacktrace.c | ||
| static_call.c | ||
| static_call_inline.c | ||
| stop_machine.c | ||
| sys.c | ||
| sys_ni.c | ||
| sysctl-test.c | ||
| sysctl.c | ||
| task_work.c | ||
| taskstats.c | ||
| torture.c | ||
| tracepoint.c | ||
| tsacct.c | ||
| ucount.c | ||
| uid16.c | ||
| uid16.h | ||
| umh.c | ||
| up.c | ||
| user-return-notifier.c | ||
| user.c | ||
| user_namespace.c | ||
| usermode_driver.c | ||
| utsname.c | ||
| utsname_sysctl.c | ||
| vhost_task.c | ||
| watch_queue.c | ||
| watchdog.c | ||
| watchdog_buddy.c | ||
| watchdog_perf.c | ||
| workqueue.c | ||
| workqueue_internal.h | ||