linux-kernel - Re: [PATCH 2/4] tools headers x86: Sync msr-index.h with kernel sources

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Date:   Fri, 12 Aug 2022 14:33:46 +0530
From:   Sandipan Das <sandipan.das@....com>
To:     Jiri Olsa <olsajiri@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        x86@...nel.org, peterz@...radead.org, bp@...en8.de,
        acme@...nel.org, namhyung@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, dave.hansen@...ux.intel.com,
        like.xu.linux@...il.com, eranian@...gle.com,
        ananth.narayan@....com, ravi.bangoria@....com,
        santosh.shukla@....com
Subject: Re: [PATCH 2/4] tools headers x86: Sync msr-index.h with kernel
 sources

Hi Jiri,

On 8/12/2022 2:03 PM, Jiri Olsa wrote:
> On Thu, Aug 11, 2022 at 06:16:47PM +0530, Sandipan Das wrote:
>> Sync msr-index.h with the kernel sources by adding the new AMD Last Branch
>> Record Extension Version 2 (LbrExtV2) MSRs.
>>
>> Signed-off-by: Sandipan Das <sandipan.das@....com>
>> ---
>>  tools/arch/x86/include/asm/msr-index.h | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/tools/arch/x86/include/asm/msr-index.h b/tools/arch/x86/include/asm/msr-index.h
>> index cc615be27a54..7f9eaf497947 100644
>> --- a/tools/arch/x86/include/asm/msr-index.h
>> +++ b/tools/arch/x86/include/asm/msr-index.h
>> @@ -574,6 +574,9 @@
>>  #define MSR_AMD64_PERF_CNTR_GLOBAL_CTL		0xc0000301
>>  #define MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_CLR	0xc0000302
>>  
>> +/* AMD Last Branch Record MSRs */
>> +#define MSR_AMD64_LBR_SELECT			0xc000010e
> 
> curious do we actualy use this in tools somewhere?
> 
> jirka
> 

Commit 9dde6cadb92b ("tools arch x86: Sync the msr-index.h copy with the kernel sources")
from Arnaldo says that adding these new MSR definitions in the tools headers allows the
beautification scripts to pick up new entries which can be used for filtering MSR access
traces.

E.g. one can trace the hardware LBR branch filter bits getting written to the LBR_SELECT
MSR while recording branches.

$ perf record -j any,u true
$ perf record -j any_call,u true

$ sudo perf trace -e msr:write_msr/max-stack=32/ --filter="msr == AMD64_LBR_SELECT"

[...]
224568.130 perf/9093 msr:write_msr(msr: AMD64_LBR_SELECT, val: 1)
                                       do_trace_write_msr ([kernel.kallsyms])
                                       do_trace_write_msr ([kernel.kallsyms])
                                       native_write_msr ([kernel.kallsyms])
                                       amd_pmu_lbr_enable_all ([kernel.kallsyms])
                                       amd_pmu_v2_enable_all ([kernel.kallsyms])
                                       x86_pmu_enable ([kernel.kallsyms])
                                       ctx_resched ([kernel.kallsyms])
                                       perf_event_exec ([kernel.kallsyms])
                                       begin_new_exec ([kernel.kallsyms])
                                       load_elf_binary ([kernel.kallsyms])
                                       bprm_execve ([kernel.kallsyms])
                                       do_execveat_common.isra.0 ([kernel.kallsyms])
                                       __x64_sys_execve ([kernel.kallsyms])
                                       do_syscall_64 ([kernel.kallsyms])
                                       entry_SYSCALL_64 ([kernel.kallsyms])
                                       execve (/usr/lib/x86_64-linux-gnu/libc.so.6)
[...]
302748.439 perf/9126 msr:write_msr(msr: AMD64_LBR_SELECT, val: 229)
                                       do_trace_write_msr ([kernel.kallsyms])
                                       do_trace_write_msr ([kernel.kallsyms])
                                       native_write_msr ([kernel.kallsyms])
                                       amd_pmu_lbr_enable_all ([kernel.kallsyms])
                                       amd_pmu_v2_enable_all ([kernel.kallsyms])
                                       x86_pmu_enable ([kernel.kallsyms])
                                       ctx_resched ([kernel.kallsyms])
                                       perf_event_exec ([kernel.kallsyms])
                                       begin_new_exec ([kernel.kallsyms])
                                       load_elf_binary ([kernel.kallsyms])
                                       bprm_execve ([kernel.kallsyms])
                                       do_execveat_common.isra.0 ([kernel.kallsyms])
                                       __x64_sys_execve ([kernel.kallsyms])
                                       do_syscall_64 ([kernel.kallsyms])
                                       entry_SYSCALL_64 ([kernel.kallsyms])
                                       execve (/usr/lib/x86_64-linux-gnu/libc.so.6)
[...]

I can add this example to the commit message in the next revision.


- Sandipan