| Message ID | 20241119153502.41361-9-vschneid@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | context_tracking,x86: Defer some IPIs until a user->kernel transition | expand |
On Tue, Nov 19, 2024 at 04:34:55PM +0100, Valentin Schneider wrote: > Later commits will cause objtool to warn about non __ro_after_init static > keys being used in .noinstr sections in order to safely defer instruction > patching IPIs targeted at NOHZ_FULL CPUs. > > __sched_clock_stable is used in .noinstr code, and can be modified at > runtime (e.g. KVM module loading). Suppressing the text_poke_sync() IPI has Wait, what !? loading KVM causes the TSC to be marked unstable?
On 20/11/24 15:59, Peter Zijlstra wrote: > On Tue, Nov 19, 2024 at 04:34:55PM +0100, Valentin Schneider wrote: >> Later commits will cause objtool to warn about non __ro_after_init static >> keys being used in .noinstr sections in order to safely defer instruction >> patching IPIs targeted at NOHZ_FULL CPUs. >> >> __sched_clock_stable is used in .noinstr code, and can be modified at >> runtime (e.g. KVM module loading). Suppressing the text_poke_sync() IPI has > > Wait, what !? loading KVM causes the TSC to be marked unstable? Ah, maybe not, I saw the below but that's actually the x86 specific stuff and IIUC can only be builtin: kvm_init_platform() `\ kvmclock_init() `\ kvm_sched_clock_init() `\ clear_sched_clock_stable() There is however this: kvm_arch_vcpu_load() `\ mark_tsc_unstable() So plugging a VCPU might do that.
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index 200e5568b9894..dc94b3717f5ce 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -76,7 +76,7 @@ static DEFINE_STATIC_KEY_FALSE_RO(sched_clock_running); * Similarly we start with __sched_clock_stable_early, thereby assuming we * will become stable, such that there's only a single 1 -> 0 transition. */ -static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable); +static DEFINE_STATIC_KEY_FALSE_FORCE(__sched_clock_stable); static int __sched_clock_stable_early = 1; /*
Later commits will cause objtool to warn about non __ro_after_init static keys being used in .noinstr sections in order to safely defer instruction patching IPIs targeted at NOHZ_FULL CPUs. __sched_clock_stable is used in .noinstr code, and can be modified at runtime (e.g. KVM module loading). Suppressing the text_poke_sync() IPI has little benefits for this key, as NOHZ_FULL is incompatible with an unstable TSC anyway. Mark it as forceful to let the kernel know to always send the text_poke_sync() IPI for it, and to let objtool know not to warn about it. Signed-off-by: Valentin Schneider <vschneid@redhat.com> --- kernel/sched/clock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)