[PATCH v2 0/2] x86, mm: minor tlb_flush tracepoint adjustments

[PATCH v2 0/2] x86, mm: minor tlb_flush tracepoint adjustments

[Tal Zussman]

One minor fix and one minor cleanup related to the tlb_flush tracepoint.

Signed-off-by: Tal Zussman <tz2294@columbia.edu>
---
Changes in v2:
- Propagated tags (thanks David, Rik, Steven!)
- Added MMU Gather maintainers to recipients
- Rebased on master
- Link to v1: https://lore.kernel.org/r/20250528-tlb-trace-fix-v1-0-2e94c58f450d@columbia.edu

---
Tal Zussman (2):
      x86/tlb/trace: Export the TLB_REMOTE_WRONG_CPU enum
      mm: Remove tlb_flush_reason::NR_TLB_FLUSH_REASONS

 include/linux/mm_types.h   | 1 -
 include/trace/events/tlb.h | 3 ++-
 2 files changed, 2 insertions(+), 2 deletions(-)
---
base-commit: d358e5254674b70f34c847715ca509e46eb81e6f
change-id: 20250528-tlb-trace-fix-eb9b6fc7bb26

Best regards,
-- 
Tal Zussman <tz2294@columbia.edu>

[PATCH v2 1/2] x86/tlb/trace: Export the TLB_REMOTE_WRONG_CPU enum

[Tal Zussman]

When the TLB_REMOTE_WRONG_CPU enum was introduced for the tlb_flush
tracepoint, the enum was not exported to userspace. Add it to the
appropriate macro definition to enable parsing by userspace tools, as
per [0].

[0] Link: https://lore.kernel.org/all/20150403013802.220157513@goodmis.org

Fixes: 2815a56e4b72 ("x86/mm/tlb: Add tracepoint for TLB flush IPI to stale CPU")
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
---
 include/trace/events/tlb.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/tlb.h b/include/trace/events/tlb.h
index b4d8e7dc38f8..725a75720a23 100644
--- a/include/trace/events/tlb.h
+++ b/include/trace/events/tlb.h
@@ -13,7 +13,8 @@
 	EM(  TLB_REMOTE_SHOOTDOWN,	"remote shootdown" )		\
 	EM(  TLB_LOCAL_SHOOTDOWN,	"local shootdown" )		\
 	EM(  TLB_LOCAL_MM_SHOOTDOWN,	"local mm shootdown" )		\
-	EMe( TLB_REMOTE_SEND_IPI,	"remote ipi send" )
+	EM(  TLB_REMOTE_SEND_IPI,	"remote ipi send" )		\
+	EMe( TLB_REMOTE_WRONG_CPU,	"remote wrong CPU" )
 
 /*
  * First define the enums in TLB_FLUSH_REASON to be exported to userspace

-- 
2.39.5

[PATCH v2 2/2] mm: Remove tlb_flush_reason::NR_TLB_FLUSH_REASONS

[Tal Zussman]

This has been unused since it was added 11 years ago in commit
d17d8f9dedb9 ("x86/mm: Add tracepoints for TLB flushes").

Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
---
 include/linux/mm_types.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 9f6de068295d..42af2292951d 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1631,7 +1631,6 @@ enum tlb_flush_reason {
 	TLB_LOCAL_MM_SHOOTDOWN,
 	TLB_REMOTE_SEND_IPI,
 	TLB_REMOTE_WRONG_CPU,
-	NR_TLB_FLUSH_REASONS,
 };
 
 /**

-- 
2.39.5

Re: [PATCH v2 1/2] x86/tlb/trace: Export the TLB_REMOTE_WRONG_CPU enum

[Lorenzo Stoakes]

On Fri, Dec 12, 2025 at 04:08:07AM -0500, Tal Zussman wrote:
> When the TLB_REMOTE_WRONG_CPU enum was introduced for the tlb_flush
> tracepoint, the enum was not exported to userspace. Add it to the
> appropriate macro definition to enable parsing by userspace tools, as
> per [0].
>
> [0] Link: https://lore.kernel.org/all/20150403013802.220157513@goodmis.org
>
> Fixes: 2815a56e4b72 ("x86/mm/tlb: Add tracepoint for TLB flush IPI to stale CPU")
> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Rik van Riel <riel@surriel.com>
> Signed-off-by: Tal Zussman <tz2294@columbia.edu>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  include/trace/events/tlb.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/trace/events/tlb.h b/include/trace/events/tlb.h
> index b4d8e7dc38f8..725a75720a23 100644
> --- a/include/trace/events/tlb.h
> +++ b/include/trace/events/tlb.h
> @@ -13,7 +13,8 @@
>  	EM(  TLB_REMOTE_SHOOTDOWN,	"remote shootdown" )		\
>  	EM(  TLB_LOCAL_SHOOTDOWN,	"local shootdown" )		\
>  	EM(  TLB_LOCAL_MM_SHOOTDOWN,	"local mm shootdown" )		\
> -	EMe( TLB_REMOTE_SEND_IPI,	"remote ipi send" )
> +	EM(  TLB_REMOTE_SEND_IPI,	"remote ipi send" )		\
> +	EMe( TLB_REMOTE_WRONG_CPU,	"remote wrong CPU" )
>
>  /*
>   * First define the enums in TLB_FLUSH_REASON to be exported to userspace
>
> --
> 2.39.5
>

Re: [PATCH v2 2/2] mm: Remove tlb_flush_reason::NR_TLB_FLUSH_REASONS

[Lorenzo Stoakes]

On Fri, Dec 12, 2025 at 04:08:08AM -0500, Tal Zussman wrote:
> This has been unused since it was added 11 years ago in commit
> d17d8f9dedb9 ("x86/mm: Add tracepoints for TLB flushes").
>
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Rik van Riel <riel@surriel.com>
> Signed-off-by: Tal Zussman <tz2294@columbia.edu>

Hmm, guess just a way of counting the number of reasons, but if nobody's using
it that's silly. So:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  include/linux/mm_types.h | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 9f6de068295d..42af2292951d 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -1631,7 +1631,6 @@ enum tlb_flush_reason {
>  	TLB_LOCAL_MM_SHOOTDOWN,
>  	TLB_REMOTE_SEND_IPI,
>  	TLB_REMOTE_WRONG_CPU,
> -	NR_TLB_FLUSH_REASONS,
>  };
>
>  /**
>
> --
> 2.39.5
>

Re: [PATCH v2 2/2] mm: Remove tlb_flush_reason::NR_TLB_FLUSH_REASONS

[Mathieu Desnoyers]

On 2025-12-15 07:40, Lorenzo Stoakes wrote:
> On Fri, Dec 12, 2025 at 04:08:08AM -0500, Tal Zussman wrote:
>> This has been unused since it was added 11 years ago in commit
>> d17d8f9dedb9 ("x86/mm: Add tracepoints for TLB flushes").
>>
>> Acked-by: David Hildenbrand <david@redhat.com>
>> Reviewed-by: Rik van Riel <riel@surriel.com>
>> Signed-off-by: Tal Zussman <tz2294@columbia.edu>
> 
> Hmm, guess just a way of counting the number of reasons, but if nobody's using
> it that's silly. So:

If TRACE_DEFINE_ENUM was implemented differently [1,2], then we could use
NR_TLB_FLUSH_REASONS in a static assert to validate that the number of
exported enum labels matches the enum tlb_flush_reason.

This would catch this kind of discrepancy at compile-time.

Thanks,

Mathieu

[1] https://github.com/lttng/lttng-modules/blob/master/include/instrumentation/events/sched.h#L132
[2] https://github.com/lttng/lttng-modules/blob/master/include/lttng/tracepoint-event-impl.h#L176

> 
-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com

Re: [PATCH v2 2/2] mm: Remove tlb_flush_reason::NR_TLB_FLUSH_REASONS

[Lorenzo Stoakes]

On Mon, Dec 15, 2025 at 08:35:58AM -0500, Mathieu Desnoyers wrote:
> On 2025-12-15 07:40, Lorenzo Stoakes wrote:
> > On Fri, Dec 12, 2025 at 04:08:08AM -0500, Tal Zussman wrote:
> > > This has been unused since it was added 11 years ago in commit
> > > d17d8f9dedb9 ("x86/mm: Add tracepoints for TLB flushes").
> > >
> > > Acked-by: David Hildenbrand <david@redhat.com>
> > > Reviewed-by: Rik van Riel <riel@surriel.com>
> > > Signed-off-by: Tal Zussman <tz2294@columbia.edu>
> >
> > Hmm, guess just a way of counting the number of reasons, but if nobody's using
> > it that's silly. So:
>
> If TRACE_DEFINE_ENUM was implemented differently [1,2], then we could use
> NR_TLB_FLUSH_REASONS in a static assert to validate that the number of
> exported enum labels matches the enum tlb_flush_reason.
>
> This would catch this kind of discrepancy at compile-time.

Sure, but for the time being this isn't being used, so dead code -> yoink!

We can obviously come back to this as necessary.

>
> Thanks,
>
> Mathieu
>
> [1] https://github.com/lttng/lttng-modules/blob/master/include/instrumentation/events/sched.h#L132
> [2] https://github.com/lttng/lttng-modules/blob/master/include/lttng/tracepoint-event-impl.h#L176
>
> >
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com

Cheers, Lorenzo