Re: [RFCv2 00/10] Linear Address Masking enabling

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	"H.J. Lu" <hjl.tools@gmail.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Alexander Potapenko <glider@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Andi Kleen <ak@linux.intel.com>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	Linux-MM <linux-mm@kvack.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFCv2 00/10] Linear Address Masking enabling
Date: Sat, 14 May 2022 01:48:16 +0300	[thread overview]
Message-ID: <20220513224816.g3uhtiq5xqgql2fs@black.fi.intel.com> (raw)
In-Reply-To: <ee786113-2173-b78b-774d-9d61d08b069b@intel.com>

On Thu, May 12, 2022 at 08:05:26PM -0700, Dave Hansen wrote:
> On 5/12/22 18:27, Thomas Gleixner wrote:
> > On Thu, May 12 2022 at 17:46, Dave Hansen wrote:
> >> On 5/12/22 17:08, H.J. Lu wrote:
> >> If I had to take a shot at this today, I think I'd opt for:
> >>
> >> 	mask = sys_enable_masking(bits=6, flags=FUZZY_NR_BITS);
> >>
> >> although I'm not super confident about the "fuzzy" flag.  I also don't
> >> think I'd totally hate the "blind" interface where the kernel just gets
> >> to pick unilaterally and takes zero input from userspace.
> > That's the only sane choice and you can make it simple for userspace:
> > 
> >        ret = prctl(GET_XXX_MASK, &mask);
> > 
> > and then let it decide based on @ret and @mask whether to use it or not.
> > 
> > But of course nobody thought about this as a generic feature and so we
> > have the ARM64 TBI muck as a precedence.
> 
> Well, not quite *nobody*:
> 
>  https://lore.kernel.org/linux-arm-kernel/7a34470c-73f0-26ac-e63d-161191d4b1e4@intel.com/

In the first RFC I tried to get ARM TBI interface generic. I resurrect it
if it fits better:

https://lore.kernel.org/all/20210205151631.43511-2-kirill.shutemov@linux.intel.com/

-- 
 Kirill A. Shutemov