linux-kernel - 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

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Message-ID: <20250416142645.4392a644.alex.williamson@redhat.com>
Date: Wed, 16 Apr 2025 14:26:45 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Salvatore Bonaccorso <carnil@...ian.org>
Cc: David Howells <dhowells@...hat.com>, Christoph Hellwig
 <hch@...radead.org>, David Hildenbrand <david@...hat.com>, Lorenzo Stoakes
 <lstoakes@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe
 <axboe@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>, Matthew Wilcox
 <willy@...radead.org>, Jan Kara <jack@...e.cz>, Jeff Layton
 <jlayton@...nel.org>, Jason Gunthorpe <jgg@...dia.com>, Logan Gunthorpe
 <logang@...tatee.com>, Hillf Danton <hdanton@...a.com>, Christian Brauner
 <brauner@...nel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Sasha
 Levin <sashal@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 regressions@...ts.linux.dev, table@...r.kernel.org, Bernd Rinn
 <bb@...n.ch>, Karri Hämäläinen
 <kh.bugreport@...look.com>, Milan Broz <gmazyland@...il.com>, Cameron
 Davidson <bugs@...idsoncj.id.au>, Markus <markus@...tz.box>
Subject: 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

On Tue, 15 Apr 2025 20:59:19 +0200
Salvatore Bonaccorso <carnil@...ian.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@...hat.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/

Thanks,
Alex