linux-kernel - Re: [PATCHv10 09/15] x86: Expose untagging mask in /proc/$PID/arch

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Message-ID: <20221018222419.oy2z2wanvwp2pnrm@box.shutemov.name>
Date:   Wed, 19 Oct 2022 01:24:19 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Taras Madan <tarasmadan@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Bharata B Rao <bharata@....com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv10 09/15] x86: Expose untagging mask in
 /proc/$PID/arch_status

On Tue, Oct 18, 2022 at 02:02:43PM -0700, Dave Hansen wrote:
> On 10/18/22 04:33, Kirill A. Shutemov wrote:
> > Add a line in /proc/$PID/arch_status to report untag_mask. It can be
> > used to find out LAM status of the process from the outside. It is
> > useful for debuggers.
> 
> Considering that address masking is not x86-specific, it seems like this
> needs a better home (another file in /proc).

In generic /proc/$PID/status?

And I'm not sure if it is a good idea at this stage. Semantics around tags
is not settled across architectures: somewhere it is per-thread, somewhere
per-process, somewhere it is global.

Maybe keep it arch-specific?

> This could even be left out of the series for now, right?  Nothing,
> including the selftests, depends on it.

GDB folks wanted to know the mask.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov