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: <aAAmQ-sRQhejItzQ@eldamar.lan>
Date: Wed, 16 Apr 2025 23:50:59 +0200
From: Salvatore Bonaccorso <carnil@...ian.org>
To: Alex Williamson <alex.williamson@...hat.com>
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,
	"stable@...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

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@...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/

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


> 
> Thanks,
> Alex
> 

-- 
  .-.  Salvatore Bonaccorso --------------- Debian GNU/Linux Developer
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