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

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Message-ID: <878rr6te6b.ffs@tglx>
Date:   Fri, 13 May 2022 03:27:24 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dave Hansen <dave.hansen@...el.com>,
        "H.J. Lu" <hjl.tools@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Linux-MM <linux-mm@...ck.org>,
        Catalin Marinas <catalin.marinas@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFCv2 00/10] Linear Address Masking enabling

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.

So much for coordination and portability...

I'm so tired of this short sighted 'cram my feature in' approach of
_all_ involved parties.

Thanks,

        tglx