linux-kernel - Re: [GIT PULL] x86/mm for 6.4

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Date:   Wed, 3 May 2023 10:01:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kirill.shutemov@...ux.intel.com
Subject: Re: [GIT PULL] x86/mm for 6.4

On Tue, May 02, 2023 at 01:14:33PM -0700, Linus Torvalds wrote:
> On Tue, May 2, 2023 at 9:00 AM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > > I guess it also wouldn't matter as much either if we hid it in a helper
> > > like the attached patch and I didn't have to read it twice. ;)
> >
> > Yeah, I think that's a good solution.
> 
> Hmm. And as I was rebasing the patch to fix up my patch, I realized
> that the current -git top-of-tree state is actually broken.
> 
> That
> 
>   #define access_ok(addr, size)                                           \
>   ({                                                                      \
>           WARN_ON_IN_IRQ();                                               \
>           likely(__access_ok(untagged_addr(addr), size));                 \
>   })
> 
> is actually *wrong* in two ways.
> 
> Now, in my original patch, I added a comment about how that
> "WARN_ON_IN_IRQ()" is bogus and this shouldn't be x86-specific at all.
> 
> I ended up going back in time to see why it was added, and I think it
> was added because we used to access 'current' in access_ok(), due to
> it using that user_addr_max() thing:
> 
>         likely(!__range_not_ok(addr, size, user_addr_max()));
> 
> but that was all removed by the set_fs() removal by Christoph Hellwig.

So I had a poke around, trying to figure out where it came from, and
yes. Commit ae31fe51a3cc ("perf/x86: Restore TASK_SIZE check on frame
pointer") is the reason that WARN_ON_IN_IRQ() thing got added.