linux-kernel - Re: [RFC 9/9] x86/mm: Implement PR_SET/GET_TAGGED_ADDR

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Date:   Sun, 7 Feb 2021 09:07:02 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     "H.J. Lu" <hjl.tools@...il.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Andi Kleen <ak@...ux.intel.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        GNU C Library <libc-alpha@...rceware.org>,
        GCC Development <gcc@....gnu.org>
Subject: Re: [RFC 9/9] x86/mm: Implement PR_SET/GET_TAGGED_ADDR_CTRL with LAM

On Fri, Feb 5, 2021 at 4:43 PM H.J. Lu <hjl.tools@...il.com> wrote:
>
> On Fri, Feb 5, 2021 at 7:16 AM Kirill A. Shutemov
> <kirill.shutemov@...ux.intel.com> wrote:
> >
> > Provide prctl() interface to enabled LAM for user addresses. Depending
> > how many tag bits requested it may result in enabling LAM_U57 or
> > LAM_U48.
>
> I prefer the alternate kernel interface based on CET arch_prctl interface which
> is implemented in glibc on users/intel/lam/master branch:
>
> https://gitlab.com/x86-glibc/glibc/-/tree/users/intel/lam/master
>
> and in GCC on users/intel/lam/master branch:
>
> https://gitlab.com/x86-gcc/gcc/-/tree/users/intel/lam/master

Hi Kirill, H.J.,

I don't have strong preference for PR_SET/GET_TAGGED_ADDR_CTRL vs
ARCH_X86_FEATURE_1_ENABLE itself, but tying LAM to ELF and
GNU_PROPERTY in the second option looks strange. LAM can be used
outside of ELF/GNU, right?