linux-kernel - [PATCH] perf/x86/amd: Run AMD BRS code only on supported hw

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Date:   Mon, 16 May 2022 17:48:38 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Stephane Eranian <eranian@...gle.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] perf/x86/amd: Run AMD BRS code only on supported hw

From: Borislav Petkov <bp@...e.de>

This fires on a Fam16h machine here:

 unchecked MSR access error: WRMSR to 0xc000010f (tried to write 0x0000000000000018) \
    at rIP: 0xffffffff81007db1 (amd_brs_reset+0x11/0x50)
 Call Trace:
  <TASK>
  amd_pmu_cpu_starting
  ? x86_pmu_dead_cpu
  x86_pmu_starting_cpu
  cpuhp_invoke_callback
  ? x86_pmu_starting_cpu
  ? x86_pmu_dead_cpu
  cpuhp_issue_call
  ? x86_pmu_starting_cpu
  __cpuhp_setup_state_cpuslocked
  ? x86_pmu_dead_cpu
  ? x86_pmu_starting_cpu
  __cpuhp_setup_state
  ? map_vsyscall
  init_hw_perf_events
  ? map_vsyscall
  do_one_initcall
  ? _raw_spin_unlock_irqrestore
  ? try_to_wake_up
  kernel_init_freeable
  ? rest_init
  kernel_init
  ret_from_fork

because that CPU hotplug callback gets executed on any AMD CPU - not
only on the BRS-enabled ones. Check the BRS feature bit properly.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/events/amd/brs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/amd/brs.c b/arch/x86/events/amd/brs.c
index 895c82165d85..bee8765a1e9b 100644
--- a/arch/x86/events/amd/brs.c
+++ b/arch/x86/events/amd/brs.c
@@ -57,7 +57,7 @@ static inline u64 get_debug_extn_cfg(void)
 
 static bool __init amd_brs_detect(void)
 {
-	if (!boot_cpu_has(X86_FEATURE_BRS))
+	if (!cpu_feature_enabled(X86_FEATURE_BRS))
 		return false;
 
 	switch (boot_cpu_data.x86) {
@@ -112,6 +112,9 @@ static inline int amd_brs_get_tos(union amd_debug_extn_cfg *cfg)
  */
 void amd_brs_reset(void)
 {
+	if (!cpu_feature_enabled(X86_FEATURE_BRS))
+		return;
+
 	/*
 	 * Reset config
 	 */
-- 
2.35.1