[PATCH] x86/cpu: Add INTEL_LUNARLAKE_M to X86_BUG_MONITOR

From: Len Brown
Date: Fri Nov 08 2024 - 08:53:04 EST


From: Len Brown <len.brown@xxxxxxxxx>

Under some conditions, MONITOR wakeups on Lunar Lake processors
can be lost, resulting in significant user-visible delays.

Add LunarLake to X86_BUG_MONITOR so that wake_up_idle_cpu()
always sends an IPI, avoiding this potential delay.

Also update the X86_BUG_MONITOR workaround to handle
the new smp_kick_mwait_play_dead() path.

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219364

Cc: stable@xxxxxxxxxxxxxxx # 6.11
Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
---
arch/x86/kernel/cpu/intel.c | 3 ++-
arch/x86/kernel/smpboot.c | 3 +++
2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index e7656cbef68d..aa63f5f780a0 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -586,7 +586,8 @@ static void init_intel(struct cpuinfo_x86 *c)
c->x86_vfm == INTEL_WESTMERE_EX))
set_cpu_bug(c, X86_BUG_CLFLUSH_MONITOR);

- if (boot_cpu_has(X86_FEATURE_MWAIT) && c->x86_vfm == INTEL_ATOM_GOLDMONT)
+ if (boot_cpu_has(X86_FEATURE_MWAIT) &&
+ (c->x86_vfm == INTEL_ATOM_GOLDMONT || c->x86_vfm == INTEL_LUNARLAKE_M))
set_cpu_bug(c, X86_BUG_MONITOR);

#ifdef CONFIG_X86_64
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 766f092dab80..910cb2d72c13 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1377,6 +1377,9 @@ void smp_kick_mwait_play_dead(void)
for (i = 0; READ_ONCE(md->status) != newstate && i < 1000; i++) {
/* Bring it out of mwait */
WRITE_ONCE(md->control, newstate);
+ /* If MONITOR unreliable, send IPI */
+ if (boot_cpu_has_bug(X86_BUG_MONITOR))
+ __apic_send_IPI(cpu, RESCHEDULE_VECTOR);
udelay(5);
}

--
2.43.0