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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 21 Nov 2018 10:43:42 -0800
Message-ID: <CAHk-=wia47WugL2b02gMx49AfpUmm5jp3tBoUL5dF2YomSGN2A@mail.gmail.com>
Subject: Re: [PATCH] x86: only use ERMS for user copies for larger sizes
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     Jens Axboe <axboe@kernel.dk>, dave.hansen@intel.com,
        pabeni@redhat.com, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, bp@alien8.de,
        Peter Anvin <hpa@zytor.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrew Lutomirski <luto@kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, dvlasenk@redhat.com,
        brgerst@gmail.com,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>
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On Wed, Nov 21, 2018 at 10:26 AM Andy Lutomirski <luto@amacapital.net> wrote:
>
> Can we maybe use this as an excuse to ask for some reasonable instructions to access user memory?

I did that long ago. It's why we have CLAC/STAC today. I was told that
what I actually asked for (get an instruction to access user space - I
suggested using a segment override prefix) was not viable.

                 Linus