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From:   Stephane Eranian <eranian@google.com>
Date:   Mon, 16 May 2022 17:59:27 -0700
Message-ID: <CABPqkBSL8BLN-mWXNJX9YYCn26kK1J-nz2B_vFjbxLPw+P1uHQ@mail.gmail.com>
Subject: Re: [PATCH] perf/x86/amd: Run AMD BRS code only on supported hw
To:     Borislav Petkov <bp@alien8.de>
Cc:     Peter Zijlstra <peterz@infradead.org>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Mon, May 16, 2022 at 8:48 AM Borislav Petkov <bp@alien8.de> wrote:
>
> From: Borislav Petkov <bp@suse.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.
>
Thanks for catching this. I tested on Zen2 (Fam17h) and it did not
trigger the problem, yet I think
the problem in amd_brs_reset() is there.

> Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-By: Stephane Eranian <eranian@google.com>

> ---
>  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
>