From: Len Brown len.brown@intel.com

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. 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@vger.kernel.org # 6.10 Signed-off-by: Len Brown len.brown@intel.com --- This is a backport of the upstream patch to Linux-6.10 and earlier --- 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 3ef4e0137d21..e6f4c16c0267 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -583,7 +583,8 @@ static void init_intel(struct cpuinfo_x86 *c) set_cpu_bug(c, X86_BUG_CLFLUSH_MONITOR);

if (c->x86 == 6 && boot_cpu_has(X86_FEATURE_MWAIT) && - ((c->x86_model == INTEL_FAM6_ATOM_GOLDMONT))) + ((c->x86_model == INTEL_FAM6_ATOM_GOLDMONT) || + (c->x86_model == INTEL_FAM6_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 0c35207320cb..ca9358acc626 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1376,6 +1376,9 @@ 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 MWAIT unreliable, send IPI */ + if (boot_cpu_has_bug(X86_BUG_MONITOR)) + __apic_send_IPI(cpu, RESCHEDULE_VECTOR); udelay(5); }