diff mbox series

x86/cpu: Add INTEL_LUNARLAKE_M to X86_BUG_MONITOR

Message ID 20241108135206.435793-3-lenb@kernel.org
State New
Headers show
Series Add Intel Lunarlake to X86_BUG_MONITOR | expand

Commit Message

Len Brown Nov. 8, 2024, 1:49 p.m. UTC 
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.

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

Comments

Peter Zijlstra Nov. 11, 2024, 4:23 p.m. UTC | #1 
On Fri, Nov 08, 2024 at 08:49:31AM -0500, Len Brown wrote:
> 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);
>  		}

Going over that code again, mwait_play_dead() is doing __mwait(.exc=0)
with IRQs disabled.

So that IPI you're trying to send there won't do no nothing :-/

Now that comment there says MCE/NMI/SMI are still open (non-maskable
etc.) so perhaps prod it on the NMI vector?

This does seem to suggest the above code path wasn't actually tested.
Perhaps mark your local machine with BUG_MONITOR, remove the md->control
WRITE_ONCE() and try kexec to test it?

Thomas, any other thoughts?
diff mbox series

Patch

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);
 		}