Re: [Patch v3 15/22] perf/x86/intel: Support SSP register capturing for arch-PEBS

[Peter Zijlstra]

On Tue, Apr 15, 2025 at 11:44:21AM +0000, Dapeng Mi wrote:
> Arch-PEBS supports to capture shadow stack pointer (SSP) register in GPR
> group. This patch supports to capture and output SSP register at
> interrupt or user space, but capturing SSP at user space requires
> 'exclude_kernel' attribute must be set. That avoids kernel space SSP
> register is captured unintentionally.
> 
> Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
> ---
>  arch/x86/events/core.c                | 15 +++++++++++++++
>  arch/x86/events/intel/core.c          |  3 ++-
>  arch/x86/events/intel/ds.c            |  9 +++++++--
>  arch/x86/events/perf_event.h          |  4 ++++
>  arch/x86/include/asm/perf_event.h     |  1 +
>  arch/x86/include/uapi/asm/perf_regs.h |  4 +++-
>  arch/x86/kernel/perf_regs.c           |  7 +++++++
>  7 files changed, 39 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 9c205a8a4fa6..0ccbe8385c7f 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -650,6 +650,21 @@ int x86_pmu_hw_config(struct perf_event *event)
>  			return -EINVAL;
>  	}
>  
> +	if (unlikely(event->attr.sample_regs_user & BIT_ULL(PERF_REG_X86_SSP))) {
> +		/* Only arch-PEBS supports to capture SSP register. */
> +		if (!x86_pmu.arch_pebs || !event->attr.precise_ip)
> +			return -EINVAL;
> +		/* Only user space is allowed to capture. */
> +		if (!event->attr.exclude_kernel)
> +			return -EINVAL;
> +	}

We should be able to support this for !PEBS samples by reading the MSR
just fine, no?

ISTR making a similar comment last time.