[resent with correct stable@vger.kernel.org list]

On Tue, Apr 15, 2025 at 08:59:19PM +0200, Salvatore Bonaccorso 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 ]

Make pin_user_pages*() leave a ZERO_PAGE unpinned if it extracts a pointer
to it from the page tables and make unpin_user_page*() correspondingly
ignore a ZERO_PAGE when unpinning.  We don't want to risk overrunning a
zero page's refcount as we're only allowed ~2 million pins on it -
something that userspace can conceivably trigger.

Add a pair of functions to test whether a page or a folio is a ZERO_PAGE.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Christoph Hellwig <hch@infradead.org>
cc: David Hildenbrand <david@redhat.com>
cc: Lorenzo Stoakes <lstoakes@gmail.com>
cc: Andrew Morton <akpm@linux-foundation.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jan Kara <jack@suse.cz>
cc: Jeff Layton <jlayton@kernel.org>
cc: Jason Gunthorpe <jgg@nvidia.com>
cc: Logan Gunthorpe <logang@deltatee.com>
cc: Hillf Danton <hdanton@sina.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: linux-fsdevel@vger.kernel.org
cc: linux-block@vger.kernel.org
cc: linux-kernel@vger.kernel.org
cc: linux-mm@kvack.org
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20230526214142.958751-2-dhowells@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: bddf10d26e6e ("uprobes: Reject the shared zeropage in uprobe_write_opcode()")
Signed-off-by: Sasha Levin <sashal@kernel.org>

Documentation/core-api/pin_user_pages.rst | 6 ++++++ include/linux/mm.h | 26 ++++++++++++++++++++++++-- mm/gup.c | 31 ++++++++++++++++++++++++++++++- 3 files changed, 60 insertions(+), 3 deletions(-)

Milan verified that the issue persists in 6.1.134 so far and the patch itself cannot be just reverted.

The failures all have a similar pattern, when pci-passthrough is used for a pci devide, for instance under qemu the bootup will fail with:

qemu-system-x86_64: -device {"driver":"vfio-pci","host":"0000:03:00.0","id":"hostdev0","bus":"pci.3","addr":"0x0"}: VFIO_MAP_DMA failed: Cannot allocate memory qemu-system-x86_64: -device {"driver":"vfio-pci","host":"0000:03:00.0","id":"hostdev0","bus":"pci.3","addr":"0x0"}: vfio 0000:03:00.0: failed to setup container

(in the case as reported by Milan).

Any ideas here?

Regards, Salvatore