linux-kernel - Re: [GIT PULL] VFIO fix for v6.0-rc5

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Date:   Fri, 9 Sep 2022 14:02:54 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] VFIO fix for v6.0-rc5

On 09.09.22 13:53, Linus Torvalds wrote:
> On Fri, Sep 9, 2022 at 6:52 AM Alex Williamson
> <alex.williamson@...hat.com> wrote:
>>
>> VFIO fix for v6.0-rc5
>>
>>   - Fix zero page refcount leak (Alex Williamson)
> 
> Ugh. This is disgusting.
> 
> Don't get me wrong - I've pulled this, but I think there's some deeper
> problem that made this patch required.
> 
> Why is pin_user_pages_remote() taking a reference to a reserved page?
> Maybe it just shouldn't (and then obviously we should fix the unpin
> case to match too).
> 
> Adding a few GUP people to the participants for comments.
> 
> Anybody?

I mentioned in an offline discussion to Alex that we should teach the 
pin/unpin interface to not mess with the zeropage at all (i.e., not 
adjust the refcount and eventually overflow it).

We decided that the unbalanced pin/unpin should be fixed independently, 
such that the refcount handling change on pin/unpin stays GUP internal.


-- 
Thanks,

David / dhildenb