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 <gmazyland@gmail.com>]

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@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).

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

Tested-by: Milan Broz <gmazyland@gmail.com>

Milan