linux-kernel - [tip: x86/mm] x86/mm/tlb: Also remove local CPU from mm

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Message-ID: <173347800117.412.912187512199282211.tip-bot2@tip-bot2>
Date: Fri, 06 Dec 2024 09:40:01 -0000
From: "tip-bot2 for Rik van Riel" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: kernel test robot <oliver.sang@...el.com>, Rik van Riel <riel@...riel.com>,
 Ingo Molnar <mingo@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: x86/mm] x86/mm/tlb: Also remove local CPU from mm_cpumask if stale

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     953753db887f9d70f70f61d6ecbe5cf209107672
Gitweb:        https://git.kernel.org/tip/953753db887f9d70f70f61d6ecbe5cf209107672
Author:        Rik van Riel <riel@...riel.com>
AuthorDate:    Thu, 05 Dec 2024 10:46:30 -05:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Fri, 06 Dec 2024 10:25:53 +01:00

x86/mm/tlb: Also remove local CPU from mm_cpumask if stale

The code in flush_tlb_func() that removes a remote CPU from the
cpumask if it is no longer running the target mm is also needed
on the originating CPU of a TLB flush, now that CPUs are no
longer cleared from the mm_cpumask at context switch time.

Flushing the TLB when we are not running the target mm is
harmless, because the CPU's tlb_gen only gets updated to
match the mm_tlb_gen, but it does hit this warning:

        WARN_ON_ONCE(local_tlb_gen > mm_tlb_gen);

  [ 210.343902][ T4668] WARNING: CPU: 38 PID: 4668 at arch/x86/mm/tlb.c:815 flush_tlb_func (arch/x86/mm/tlb.c:815)

Removing both local and remote CPUs from the mm_cpumask
when doing a flush for a not currently loaded mm avoids
that warning.

Reported-by: kernel test robot <oliver.sang@...el.com>
Tested-by: kernel test robot <oliver.sang@...el.com>
Signed-off-by: Rik van Riel <riel@...riel.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: https://lore.kernel.org/r/20241205104630.755706ca@fangorn
Closes: https://lore.kernel.org/oe-lkp/202412051551.690e9656-lkp@intel.com
---
 arch/x86/mm/tlb.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 1aac4fa..3c30817 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -756,13 +756,13 @@ static void flush_tlb_func(void *info)
 	if (!local) {
 		inc_irq_stat(irq_tlb_count);
 		count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
+	}
 
-		/* Can only happen on remote CPUs */
-		if (f->mm && f->mm != loaded_mm) {
-			cpumask_clear_cpu(raw_smp_processor_id(), mm_cpumask(f->mm));
-			trace_tlb_flush(TLB_REMOTE_WRONG_CPU, 0);
-			return;
-		}
+	/* The CPU was left in the mm_cpumask of the target mm. Clear it. */
+	if (f->mm && f->mm != loaded_mm) {
+		cpumask_clear_cpu(raw_smp_processor_id(), mm_cpumask(f->mm));
+		trace_tlb_flush(TLB_REMOTE_WRONG_CPU, 0);
+		return;
 	}
 
 	if (unlikely(loaded_mm == &init_mm))