linux-kernel - Re: [PATCHv3 7/8] x86: Expose untagging mask in /proc/$PID/arch

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Date:   Sat, 11 Jun 2022 04:28:30 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
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>,
        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>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 7/8] x86: Expose untagging mask in
 /proc/$PID/arch_status

On Fri, Jun 10, 2022 at 08:24:38AM -0700, Dave Hansen wrote:
> On 6/10/22 07:35, Kirill A. Shutemov wrote:
> > +/*
> > + * Report architecture specific information
> > + */
> > +int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns,
> > +			struct pid *pid, struct task_struct *task)
> > +{
> > +	/*
> > +	 * Report AVX512 state if the processor and build option supported.
> > +	 */
> > +	if (cpu_feature_enabled(X86_FEATURE_AVX512F))
> > +		avx512_status(m, task);
> > +
> > +	seq_printf(m, "untag_mask:\t%#lx\n", mm_untag_mask(task->mm));
> > +
> > +	return 0;
> > +}
> 
> Arch-specific gunk is great for, well, arch-specific stuff.  AVX-512 and
> its, um, "quirks", really won't show up anywhere else.  But x86 isn't
> even the first to be doing this address tagging business.
> 
> Shouldn't we be talking to the ARM folks about a common way to do this?

+ Catalin, Will.

I guess we can expose the mask via proc for ARM too, but I'm not sure if
we can unify interface further without breaking existing TBI users: TBI is
enabled per-thread while LAM is per-process.

Any opinions?

-- 
 Kirill A. Shutemov