* Alexey Dobriyan <adobri...@gmail.com> wrote:
> clear_user() used MOVQ+MOVB and if MOVQ faults, code simply exits and
> honestly returns remaining length. In case of unaligned area, unaligned
> remainder would count towards return value (correctly) but not cleared
> (lazy code at least):
>
> clear_user(p + 4096 - 4, 8) = 8
>
> No one would have noticed but REP MOVSB addition to clear_user()
> repertoire creates a problem: REP MOVSB does everything correctly,
> clears and counts to the last possible byte, but REP STOSQ and MOVQ
> variants DO NOT:
>
> MOVQ clear_user(p + 4096 - 4, 8) = 8
> REP STOSQ clear_user(p + 4096 - 4, 8) = 8
> REP STOSB clear_user(p + 4096 - 4, 8) = 4
>
> Patch fixes incomplete clear on 32-bit and 64-bit REP STOSQ, MOVQ.
So please flip the order of the changes around so that we never have this
inconsistency observable: i.e. first update the existing clearing method, then
move it and introduce the new variants without having to patch them.
Thanks,
Ingo
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