linux-kernel - [tip: perf/urgent] x86/perf: Fix snapshot_branch

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Date:   Wed, 17 Nov 2021 13:59:52 -0000
From:   "tip-bot2 for Song Liu" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Song Liu <songliubraving@...com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Like Xu <likexu@...cent.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] x86/perf: Fix snapshot_branch_stack warning in VM

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     f3fd84a3b7754b60df67ebfe64e1d90623895111
Gitweb:        https://git.kernel.org/tip/f3fd84a3b7754b60df67ebfe64e1d90623895111
Author:        Song Liu <songliubraving@...com>
AuthorDate:    Thu, 11 Nov 2021 21:45:10 -08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 17 Nov 2021 14:48:43 +01:00

x86/perf: Fix snapshot_branch_stack warning in VM

When running in VM intel_pmu_snapshot_branch_stack triggers WRMSR warning
like:

 [ ] unchecked MSR access error: WRMSR to 0x3f1 (tried to write 0x0000000000000000) at rIP: 0xffffffff81011a5b (intel_pmu_snapshot_branch_stack+0x3b/0xd0)

This can be triggered with BPF selftests:

  tools/testing/selftests/bpf/test_progs -t get_branch_snapshot

This warning is caused by __intel_pmu_pebs_disable_all() in the VM.
Since it is not necessary to disable PEBS for LBR, remove it from
intel_pmu_snapshot_branch_stack and intel_pmu_snapshot_arch_branch_stack.

Fixes: c22ac2a3d4bd ("perf: Enable branch record for software events")
Signed-off-by: Song Liu <songliubraving@...com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Like Xu <likexu@...cent.com>
Link: https://lore.kernel.org/r/20211112054510.2667030-1-songliubraving@fb.com
---
 arch/x86/events/intel/core.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 42cf01e..ec6444f 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2211,7 +2211,6 @@ intel_pmu_snapshot_branch_stack(struct perf_branch_entry *entries, unsigned int 
 	/* must not have branches... */
 	local_irq_save(flags);
 	__intel_pmu_disable_all(false); /* we don't care about BTS */
-	__intel_pmu_pebs_disable_all();
 	__intel_pmu_lbr_disable();
 	/*            ... until here */
 	return __intel_pmu_snapshot_branch_stack(entries, cnt, flags);
@@ -2225,7 +2224,6 @@ intel_pmu_snapshot_arch_branch_stack(struct perf_branch_entry *entries, unsigned
 	/* must not have branches... */
 	local_irq_save(flags);
 	__intel_pmu_disable_all(false); /* we don't care about BTS */
-	__intel_pmu_pebs_disable_all();
 	__intel_pmu_arch_lbr_disable();
 	/*            ... until here */
 	return __intel_pmu_snapshot_branch_stack(entries, cnt, flags);