linux-kernel - Re: [PATCH] x86: only use ERMS for user copies for larger sizes

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Message-ID: <CAHk-=wia47WugL2b02gMx49AfpUmm5jp3tBoUL5dF2YomSGN2A@mail.gmail.com>
Date:   Wed, 21 Nov 2018 10:43:42 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Jens Axboe <axboe@...nel.dk>, dave.hansen@...el.com,
        pabeni@...hat.com, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, bp@...en8.de,
        Peter Anvin <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>, dvlasenk@...hat.com,
        brgerst@...il.com,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: only use ERMS for user copies for larger sizes

On Wed, Nov 21, 2018 at 10:26 AM Andy Lutomirski <luto@...capital.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