linux-kernel - [PATCH] perf/x86/intel: Fix and clean up intel_pmu_drain_arch

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Message-ID: <aRRcyoOobRyam5yD@gmail.com>
Date: Wed, 12 Nov 2025 11:09:14 +0100
From: Ingo Molnar <mingo@...nel.org>
To: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
Cc: Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: [PATCH] perf/x86/intel: Fix and clean up intel_pmu_drain_arch_pebs()
 type use


* Mi, Dapeng <dapeng1.mi@...ux.intel.com> wrote:

> 
> On 11/12/2025 12:42 PM, Stephen Rothwell wrote:
> > Hi all,
> >
> > After merging the tip tree, today's linux-next build (i386 defconfig)
> > failed like this:
> >
> > arch/x86/events/intel/ds.c: In function 'intel_pmu_drain_arch_pebs':
> > arch/x86/events/intel/ds.c:2983:24: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
> >  2983 |         top = (void *)((u64)cpuc->pebs_vaddr +
> >       |                        ^
> > arch/x86/events/intel/ds.c:2983:15: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
> >  2983 |         top = (void *)((u64)cpuc->pebs_vaddr +
> >       |               ^
> > cc1: all warnings being treated as errors
> 
> Thanks for reporting the issue. I suppose the below patch would fix the
> building error. I would post it as an independent patch later.
> 
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index c93bf971d97b..f695de9f7049 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -2979,7 +2979,7 @@ static void intel_pmu_drain_arch_pebs(struct pt_regs
> *iregs,
>         }
> 
>         base = cpuc->pebs_vaddr;
> -       top = (void *)((u64)cpuc->pebs_vaddr +
> +       top = (void *)((unsigned long)cpuc->pebs_vaddr +
>                        (index.wr << ARCH_PEBS_INDEX_WR_SHIFT));

This doesn't really address the core issue: ugly, fragile code due to 
type confusion. The proper fix is:

	top = cpuc->pebs_vaddr + (index.wr << ARCH_PEBS_INDEX_WR_SHIFT);

which is also much cleaner, see:

	60f9f1d43720 ("perf/x86/intel: Fix and clean up intel_pmu_drain_arch_pebs() type use")

(also attached below.)

All this should be resolved in the latest -tip tree.

Thanks,

	Ingo

=====================>
>From 60f9f1d437201f6c457fc8a56f9df6d8a6d0bea6 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@...nel.org>
Date: Wed, 12 Nov 2025 10:40:26 +0100
Subject: [PATCH] perf/x86/intel: Fix and clean up intel_pmu_drain_arch_pebs() type use

The following commit introduced a build failure on x86-32:

  2721e8da2de7 ("perf/x86/intel: Allocate arch-PEBS buffer and initialize PEBS_BASE MSR")

  ...

  arch/x86/events/intel/ds.c:2983:24: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]

The forced type conversion to 'u64' and 'void *' are not 32-bit clean,
but they are also entirely unnecessary: ->pebs_vaddr is 'void *' already,
and integer-compatible pointer arithmetics will work just fine on it.

Fix & simplify the code.

Fixes: 2721e8da2de7 ("perf/x86/intel: Allocate arch-PEBS buffer and initialize PEBS_BASE MSR")
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Kan Liang <kan.liang@...ux.intel.com>
Cc: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Link: https://patch.msgid.link/20251029102136.61364-10-dapeng1.mi@linux.intel.com
---
 arch/x86/events/intel/ds.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index c93bf971d97b..2e170f2093ac 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -2979,8 +2979,7 @@ static void intel_pmu_drain_arch_pebs(struct pt_regs *iregs,
 	}
 
 	base = cpuc->pebs_vaddr;
-	top = (void *)((u64)cpuc->pebs_vaddr +
-		       (index.wr << ARCH_PEBS_INDEX_WR_SHIFT));
+	top = cpuc->pebs_vaddr + (index.wr << ARCH_PEBS_INDEX_WR_SHIFT);
 
 	index.wr = 0;
 	index.full = 0;