linux-kernel - Re: [PATCH 6.6.y 0/4] perf/x86/amd: add LBR capture support outside of hardware events

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Message-ID: <72a635cb-05c7-47d2-84aa-4d82d1e0aebd@linux.dev>
Date: Thu, 8 Jan 2026 21:53:46 +0800
From: Leon Hwang <leon.hwang@...ux.dev>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: stable@...r.kernel.org, Andrii Nakryiko <andrii@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
 Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>,
 Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H . Peter Anvin" <hpa@...or.com>, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6.6.y 0/4] perf/x86/amd: add LBR capture support outside
 of hardware events

On 2026/1/8 19:11, Greg KH wrote:
> On Fri, Jan 02, 2026 at 05:03:16PM +0800, Leon Hwang wrote:
>> Hi all,
>>
>> This backport wires up AMD perfmon v2 so BPF and other software clients
>> can snapshot LBR stacks on demand, similar to the Intel support
>> upstream. The series keeps the LBR-freeze path branchless, adds the
>> perf_snapshot_branch_stack callback for AMD, and drops the
>> sampling-only restriction now that snapshots can be taken from software
>> contexts.
>>
>> Leon Hwang (4):
>>   perf/x86/amd: Ensure amd_pmu_core_disable_all() is always inlined
>>   perf/x86/amd: Avoid taking branches before disabling LBR
>>   perf/x86/amd: Support capturing LBR from software events
>>   perf/x86/amd: Don't reject non-sampling events with configured LBR
> 
> 
> Why is this for a stable kernel?  Isn't it a new feature?  If you need
> this feature, why not use a newer kernel tree?
> 

This series enables LBR snapshot support on AMD CPUs.

You are right that this is not a bug fix but a feature enablement.
If backporting this to the stable tree is not appropriate, that is
totally fine. In that case, I will carry these changes in our in-house
stable kernel instead.

Thanks for the clarification.

Thanks,
Leon

> thanks,
> 
> greg k-h