[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen staging-4.19] x86/idle: Fix buggy "x86/mwait-idle: enable interrupts before C1 on Xeons"
commit 67bb8f699dfaea3f6de0d7110b22b1bdfc2d838a Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> AuthorDate: Wed Jul 2 14:51:38 2025 +0100 Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> CommitDate: Mon Jul 7 22:52:15 2025 +0100 x86/idle: Fix buggy "x86/mwait-idle: enable interrupts before C1 on Xeons" The check of this_softirq_pending must be performed with irqs disabled, but this property was broken by an attempt to optimise entry/exit latency. Commit c227233ad64c in Linux (which we copied into Xen) was fixed up by edc8fc01f608 in Linux, which we have so far missed. Going to sleep without waking on interrupts is nonsensical outside of play_dead(), so overload this to select between two possible MWAITs, the second using the STI shadow to cover MWAIT for exactly the same reason as we do in safe_halt(). Fixes: b17e0ec72ede ("x86/mwait-idle: enable interrupts before C1 on Xeons") Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> (cherry picked from commit 9b0f0f6e235618c2764e925b58c4bfe412730ced) --- xen/arch/x86/acpi/cpu_idle.c | 16 +++++++++++++++- xen/arch/x86/cpu/mwait-idle.c | 8 ++------ 2 files changed, 17 insertions(+), 7 deletions(-) diff --git a/xen/arch/x86/acpi/cpu_idle.c b/xen/arch/x86/acpi/cpu_idle.c index 176df1ed17..69857a58ef 100644 --- a/xen/arch/x86/acpi/cpu_idle.c +++ b/xen/arch/x86/acpi/cpu_idle.c @@ -79,6 +79,13 @@ static always_inline void mwait(unsigned int eax, unsigned int ecx) :: "a" (eax), "c" (ecx) ); } +static always_inline void sti_mwait_cli(unsigned int eax, unsigned int ecx) +{ + /* STI shadow covers MWAIT. */ + asm volatile ( "sti; mwait; cli" + :: "a" (eax), "c" (ecx) ); +} + #define GET_HW_RES_IN_NS(msr, val) \ do { rdmsrl(msr, val); val = tsc_ticks2ns(val); } while( 0 ) #define GET_MC6_RES(val) GET_HW_RES_IN_NS(0x664, val) @@ -473,12 +480,19 @@ void mwait_idle_with_hints(unsigned int eax, unsigned int ecx) monitor(this_softirq_pending, 0, 0); + ASSERT(!local_irq_is_enabled()); + if ( !*this_softirq_pending ) { struct cpu_info *info = get_cpu_info(); spec_ctrl_enter_idle(info); - mwait(eax, ecx); + + if ( ecx & MWAIT_ECX_INTERRUPT_BREAK ) + mwait(eax, ecx); + else + sti_mwait_cli(eax, ecx); + spec_ctrl_exit_idle(info); } diff --git a/xen/arch/x86/cpu/mwait-idle.c b/xen/arch/x86/cpu/mwait-idle.c index 182518528a..3c63f0d45a 100644 --- a/xen/arch/x86/cpu/mwait-idle.c +++ b/xen/arch/x86/cpu/mwait-idle.c @@ -962,12 +962,8 @@ static void cf_check mwait_idle(void) update_last_cx_stat(power, cx, before); - if (cx->irq_enable_early) - local_irq_enable(); - - mwait_idle_with_hints(cx->address, MWAIT_ECX_INTERRUPT_BREAK); - - local_irq_disable(); + mwait_idle_with_hints(cx->address, + cx->irq_enable_early ? 0 : MWAIT_ECX_INTERRUPT_BREAK); after = alternative_call(cpuidle_get_tick); -- generated by git-patchbot for /home/xen/git/xen.git#staging-4.19
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