linux-kernel - Re: [GIT PULL] x86/mm for 6.2

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Message-ID: <CAHk-=whjCVDeVa8jxEjnimfhKNnXiku7ku4NirmY+poKsnM5HQ@mail.gmail.com>
Date:   Fri, 16 Dec 2022 09:43:11 -0600
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     kirill.shutemov@...ux.intel.com,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org, jejb@...ux.ibm.com,
        martin.petersen@...cle.com
Subject: Re: [GIT PULL] x86/mm for 6.2

On Fri, Dec 16, 2022 at 9:05 AM Kirill A. Shutemov <kirill@...temov.name> wrote:
>
> Below is preliminary fixup that suppose to address the issue. It does not
> include change to untagged_addr() interface to avoid the clutter.

Looks like the right direction.

And once you change untagged_addr() to take 'tsk', you should then be
able to cache all the information in the thread struct, and avoid the
'tsk->mm' dereference entirely.

> kthread_use_mm() should be safe as long as no arch actually implements
> per-thread tagging enabling.

I think in a perfect world the (few) users of kthread_use_mm() would
also just make sure they did the locking of thing, so that they can't
have that race with somebody that then would enable LAM later.

             Linus