Re: [PATCH] [core-for-CI PATCH] x86/apic: Stop the TSC Deadline timer during lapic timer shutdown

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Mon, Oct 07, 2024 at 07:22:42PM +0530, Karthik Poosa wrote:
> From: Zhang Rui <rui.zhang@intel.com>
> 
> This is a core-for-CI patch for
> https://lore.kernel.org/all/20240929063521.17284-1-rui.zhang@intel.com/
> 
> According to Intel SDM, for the local APIC timer,
> 1. "The initial-count register is a read-write register. A write of 0 to
>    the initial-count register effectively stops the local APIC timer, in
>    both one-shot and periodic mode."
> 2. "In TSC deadline mode, writes to the initial-count register are
>    ignored; and current-count register always reads 0. Instead, timer
>    behavior is controlled using the IA32_TSC_DEADLINE MSR."
>    "In TSC-deadline mode, writing 0 to the IA32_TSC_DEADLINE MSR disarms
>    the local-APIC timer."
> 
> Current code in lapic_timer_shutdown() writes 0 to the initial-count
> register. This stops the local APIC timer for one-shot and periodic mode
> only. In TSC deadline mode, the timer is not properly stopped.
> 
> Some CPUs are affected by this and they are woke up by the armed timer
> in s2idle in TSC deadline mode.
> 
> Stop the TSC deadline timer in lapic_timer_shutdown() by writing 0 to
> MSR_IA32_TSC_DEADLINE.
> 
> Fixes: 279f1461432c ("x86: apic: Use tsc deadline for oneshot when available")
> Link: https://lore.kernel.org/all/20240929063521.17284-1-rui.zhang@intel.com/

The problem I see here is that this seems stalled. No review there. Is that merged
in some branch and moving upstream and to stable?

Cc: Zhang Rui <rui.zhang@intel.com>

> References: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12344

The right reference link we should have in this topic/core-for-CI patch
is: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2766
showing the why we need the patch.

https://drm.pages.freedesktop.org/maintainer-tools/committer/core-for-CI.html

But was this really confirmed?

Anyway, I'm hesitant here mostly because I don't believe we should add this patch
if that is not getting propagated to Linus and/or stable trees.

> Signed-off-by: Zhang Rui <rui.zhang@intel.com>
> Signed-off-by: Karthik Poosa <karthik.poosa@intel.com>
> 
> ---
>  arch/x86/kernel/apic/apic.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 6513c53c9459..d1006531729a 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -441,6 +441,10 @@ static int lapic_timer_shutdown(struct clock_event_device *evt)
>  	v |= (APIC_LVT_MASKED | LOCAL_TIMER_VECTOR);
>  	apic_write(APIC_LVTT, v);
>  	apic_write(APIC_TMICT, 0);
> +
> +	if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER))
> +		wrmsrl(MSR_IA32_TSC_DEADLINE, 0);
> +
>  	return 0;
>  }
>  
> -- 
> 2.25.1
>