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);
 		}
 
-- 
2.43.0

On Fri, Nov 08 2024 at 08:49, Len Brown wrote:
> 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

You either fail to understand or intentionally ignore the process for
stable backports, which is in place since more than a decade.

Documentation/process/* has plenty of information how that works and
you're around long enough to know that already.

I don't care about you wasting your time, but I very much care about you
wasting my time to deal with pointless emails. I get plenty enough of
them every day.

Thanks,

        tglx