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

[Alex Williamson]

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/

Thanks,
Alex