Re: [regression 6.1.y] Regression from 476c1dfefab8 ("mm: Don't pin ZERO_PAGE in pin_user_pages()") with pci-passthrough for both KVM VMs and booting in xen DomU

[Salvatore Bonaccorso <carnil@debian.org>]

Hi Alex,

On Wed, Apr 16, 2025 at 02:26:45PM -0600, Alex Williamson wrote:
> On Tue, 15 Apr 2025 20:59:19 +0200
> Salvatore Bonaccorso <carnil@debian.org> wrote:
> 
> > Hi
> > 
> > [Apologies if this has been reported already but I have not found an
> > already filled corresponding report]
> > 
> > After updating from the 6.1.129 based version to 6.1.133, various
> > users have reported that their VMs do not boot anymore up (both KVM
> > and under Xen) if pci-passthrough is involved. The reports are at:
> > 
> > https://bugs.debian.org/1102889
> > https://bugs.debian.org/1102914
> > https://bugs.debian.org/1103153
> > 
> > Milan Broz bisected the issues and found that the commit introducing
> > the problems can be tracked down to backport of c8070b787519 ("mm:
> > Don't pin ZERO_PAGE in pin_user_pages()") from 6.5-rc1 which got
> > backported as 476c1dfefab8 ("mm: Don't pin ZERO_PAGE in
> > pin_user_pages()") in 6.1.130. See https://bugs.debian.org/1102914#60
> > 
> > #regzbot introduced: 476c1dfefab8b98ae9c3e3ad283c2ac10d30c774
> > 
> > 476c1dfefab8b98ae9c3e3ad283c2ac10d30c774 is the first bad commit
> > commit 476c1dfefab8b98ae9c3e3ad283c2ac10d30c774
> > Author: David Howells <dhowells@redhat.com>
> > Date:   Fri May 26 22:41:40 2023 +0100
> > 
> >     mm: Don't pin ZERO_PAGE in pin_user_pages()
> > 
> >     [ Upstream commit c8070b78751955e59b42457b974bea4a4fe00187 ]
> 
> It's a bad backport, I've debugged and posted the fix for stable here:
> 
> https://lore.kernel.org/all/20250416202441.3911142-1-alex.williamson@redhat.com/

Thank you, that worked (replying here as well mainly to fix my mistake
in the CC to stable@vger.kernel.org, which got truncated to
table@vger.kernel.org in my initial submission).


> 
> Thanks,
> Alex
> 

-- 
  .-.  Salvatore Bonaccorso --------------- Debian GNU/Linux Developer
  oo|  ----------------------------------------- http://www.debian.org
 /`'\  GPG key ID: 0x789D6F057FD863FE --------------------------------
(\_;/) Fingerprint: 04A4 407C B914 2C23 030C  17AE 789D 6F05 7FD8 63FE