Re: [PATCHv3 7/8] x86: Expose untagging mask in /proc/$PID/arch_status

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Dave Hansen <dave.hansen@intel.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	x86@kernel.org, Kostya Serebryany <kcc@google.com>,
	Andrey Ryabinin <ryabinin.a.a@gmail.com>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	"H . J . Lu" <hjl.tools@gmail.com>,
	Andi Kleen <ak@linux.intel.com>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCHv3 7/8] x86: Expose untagging mask in /proc/$PID/arch_status
Date: Sat, 11 Jun 2022 04:28:30 +0300	[thread overview]
Message-ID: <20220611012830.hs437yikbjgwlije@black.fi.intel.com> (raw)
In-Reply-To: <144af1ab-1e7e-b75c-331c-d9c2e55b9062@intel.com>

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