linux-kernel - Re: [kvm-unit-tests Patch v3 02/11] x86: pmu: Enlarge cnt[] length to 64 in check_counters

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Date: Mon, 25 Mar 2024 14:41:31 -0700
From: Jim Mattson <jmattson@...gle.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Zhenyu Wang <zhenyuw@...ux.intel.com>, 
	Zhang Xiong <xiong.y.zhang@...el.com>, Mingwei Zhang <mizhang@...gle.com>, 
	Like Xu <like.xu.linux@...il.com>, Jinrong Liang <cloudliang@...cent.com>, 
	Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [kvm-unit-tests Patch v3 02/11] x86: pmu: Enlarge cnt[] length to
 64 in check_counters_many()

On Tue, Jan 2, 2024 at 7:09 PM Dapeng Mi <dapeng1.mi@...ux.intel.com> wrote:
>
> Considering there are already 8 GP counters and 4 fixed counters on
> latest Intel processors, like Sapphire Rapids. The original cnt[] array
> length 10 is definitely not enough to cover all supported PMU counters on these
> new processors even through currently KVM only supports 3 fixed counters
> at most. This would cause out of bound memory access and may trigger
> false alarm on PMU counter validation
>
> It's probably more and more GP and fixed counters are introduced in the
> future and then directly extends the cnt[] array length to 64 once and
> for all.
>
> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> ---
>  x86/pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/x86/pmu.c b/x86/pmu.c
> index 0def28695c70..a13b8a8398c6 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -254,7 +254,7 @@ static void check_fixed_counters(void)
>
>  static void check_counters_many(void)
>  {
> -       pmu_counter_t cnt[10];
> +       pmu_counter_t cnt[64];

I think 48 should be sufficient, based on the layout of
IA32_PERF_GLOBAL_CTRL and IA32_PERF_GLOBAL_STATUS.

In any event, let's bump this up!

Reviewed-by: Jim Mattson <jmattson@...gle.com>