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

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Message-ID: <CAGudoHHOEMvz6=JZ2XZYKgKTqQ-FeCcXxVEvS2xBncn-ck5JXg@mail.gmail.com>
Date:   Sun, 3 Sep 2023 23:18:44 +0200
From:   Mateusz Guzik <mjguzik@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        bp@...en8.de
Subject: Re: [PATCH v2] x86: bring back rep movsq for user access on CPUs
 without ERMS

On 9/3/23, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Sun, 3 Sept 2023 at 14:06, Mateusz Guzik <mjguzik@...il.com> wrote:
>>
>> I don't think it is *that* bad. I did a quick sanity check on that
>> front by rolling with bpftrace on cases which pass AT_EMPTY_PATH *and*
>> provide a path.
>
> I guess you are right - nobody sane would use AT_EMPTY_PATH except if
> they don't have a path.
>
> Of course, the only reason we're discussing this in the first place is
> because people are doing insane things, which makes _that_ particular
> argument very weak indeed...
>

I put blame on whoever allowed non-NULL path and AT_EMPTY_PATH as a
valid combination, forcing the user buf to be accessed no matter what.
But I'm not going to go digging for names. ;)

-- 
Mateusz Guzik <mjguzik gmail.com>