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

[Milan Broz]

On 4/16/25 11:50 PM, Salvatore Bonaccorso wrote:
> 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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > 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@xxxxxxxxxx/
>
> Thank you, that worked (replying here as well mainly to fix my mistake
> in the CC to stable@xxxxxxxxxxxxxxx, which got truncated to
> table@xxxxxxxxxxxxxxx in my initial submission).

I can also confirm the fix works, thanks for the quick response!

Tested-by: Milan Broz <gmazyland@xxxxxxxxx>

Milan