linux-kernel - Re: [PATCH v2] x86: bring back rep movsq for user access on CPUs without ERMS

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Message-ID: <CAHk-=whC8TaarEhz2ie_w01r34hQHNCTiZLAs6e42ewP7+cvoA@mail.gmail.com>
Date:   Tue, 12 Sep 2023 13:48:04 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     Mateusz Guzik <mjguzik@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "bp@...en8.de" <bp@...en8.de>
Subject: Re: [PATCH v2] x86: bring back rep movsq for user access on CPUs
 without ERMS

On Tue, 12 Sept 2023 at 12:41, David Laight <David.Laight@...lab.com> wrote:
>
> What I found seemed to imply that 'rep movsq' used the same internal
> logic as 'rep movsb' (pretty easy to do in hardware)

Christ.

I told you. It's pretty easy in hardware  AS LONG AS IT'S ALIGNED.

And if it's unaligned, "rep movsq" is FUNDAMENTALLY HARDER.

Really.

                    Linus