linux-kernel - Re: [PATCH V9 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE

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Message-ID: <20201009095300.GI2628@hirez.programming.kicks-ass.net>
Date:   Fri, 9 Oct 2020 11:53:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will@...nel.org>
Cc:     kan.liang@...ux.intel.com, mingo@...hat.com, acme@...nel.org,
        linux-kernel@...r.kernel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        eranian@...gle.com, ak@...ux.intel.com, dave.hansen@...el.com,
        kirill.shutemov@...ux.intel.com, mpe@...erman.id.au,
        benh@...nel.crashing.org, paulus@...ba.org,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH V9 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE

On Fri, Oct 09, 2020 at 10:37:51AM +0100, Will Deacon wrote:
> On Fri, Oct 09, 2020 at 11:09:27AM +0200, Peter Zijlstra wrote:

> > Patch 4 makes it all far worse by exposing it to pretty much everybody.
> > 
> > Now, I think we can fix at least the user mappings with the below delta,
> > but if archs are using non-page-table MMU sizes we'll need arch helpers.
> > 
> > ARM64 is in that last boat.
> > 
> > Will, can you live with the below, if not, what would you like to do,
> > make the entire function __weak so that you can override it, or hook
> > into it somewhere?
> 
> Hmm, so I don't think we currently have any PMUs that set 'data->addr'
> on arm64, in which case maybe none of this currently matters for us.
> 
> However, I must admit that I couldn't figure out exactly what gets exposed
> to userspace when the backend drivers don't look at the sample_type or
> do anything with the addr field.

Patch 4:

  https://lkml.kernel.org/r/20201001135749.2804-5-kan.liang@linux.intel.com

is the one that exposes this to everybody with perf support. It will
then report the page-size for the code address (SAMPLE_IP).