Re: [PATCH 2/8] perf/x86/amd/ibs: Add workaround for erratum #1,197

[Namhyung Kim]

Hello,

On Tue, Aug 17, 2021 at 3:11 PM Kim Phillips <kim.phillips@xxxxxxx> wrote:
>
> Erratum #1197 "IBS (Instruction Based Sampling) Register State May be
> Incorrect After Restore From CC6" is published in a document available
> at the link tag below:
>
> "Revision Guide for AMD Family 19h Models 00h-0Fh Processors"
> 56683 Rev. 1.04 July 2021
>
> Implement the erratum's suggested workaround and ignore IBS samples
> if MSRC001_1031 == 0.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
> Signed-off-by: Kim Phillips <kim.phillips@xxxxxxx>
> Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Cc: Andrew Murray <amurray@xxxxxxxxxxxxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Ian Rogers <irogers@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: Joao Martins <joao.m.martins@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Michael Petlan <mpetlan@xxxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Robert Richter <robert.richter@xxxxxxx>
> Cc: Stephane Eranian <eranian@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-perf-users@xxxxxxxxxxxxxxx
> Cc: x86@xxxxxxxxxx
> ---
>  arch/x86/events/amd/ibs.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
> index 8c25fbd5142e..222c890527a2 100644
> --- a/arch/x86/events/amd/ibs.c
> +++ b/arch/x86/events/amd/ibs.c
> @@ -90,6 +90,7 @@ struct perf_ibs {
>         unsigned long                   offset_mask[1];
>         int                             offset_max;
>         unsigned int                    fetch_count_reset_broken : 1;
> +       unsigned int                    fetch_ignore_if_zero_rip : 1;
>         struct cpu_perf_ibs __percpu    *pcpu;
>
>         struct attribute                **format_attrs;
> @@ -673,6 +674,10 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
>         if (check_rip && (ibs_data.regs[2] & IBS_RIP_INVALID)) {
>                 regs.flags &= ~PERF_EFLAGS_EXACT;
>         } else {
> +               /* Workaround for erratum #1,197 */
> +               if (perf_ibs->fetch_ignore_if_zero_rip && !(ibs_data.regs[1]))
> +                       goto out;

Can we just use the iregs.ip instead of dropping the sample?
Users might care about the accurate number of samples..

Thanks,
Namhyung


> +
>                 set_linear_ip(&regs, ibs_data.regs[1]);
>                 regs.flags |= PERF_EFLAGS_EXACT;
>         }
> @@ -770,6 +775,9 @@ static __init void perf_event_ibs_init(void)
>         if (boot_cpu_data.x86 >= 0x16 && boot_cpu_data.x86 <= 0x18)
>                 perf_ibs_fetch.fetch_count_reset_broken = 1;
>
> +       if (boot_cpu_data.x86 == 0x19 && boot_cpu_data.x86_model < 0x10)
> +               perf_ibs_fetch.fetch_ignore_if_zero_rip = 1;
> +
>         perf_ibs_pmu_init(&perf_ibs_fetch, "ibs_fetch");
>
>         if (ibs_caps & IBS_CAPS_OPCNT) {
> --
> 2.31.1
>