FAILED: patch "[PATCH] vfio/pci: Restore 8-byte ioeventfd support" failed to apply to 6.18-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x b30b52c2fb82e6d38ee2845a4d85e8254b44f3d8
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107050755-failed-6.18-b30b52c2fb82@kernel.org' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From b30b52c2fb82e6d38ee2845a4d85e8254b44f3d8 Mon Sep 17 00:00:00 2001
From: Li RongQing <lirongqing@baidu.com>
Date: Tue, 22 Sep 2026 12:00:13 +0800
Subject: [PATCH] vfio/pci: Restore 8-byte ioeventfd support

Commit b44a06bd28f2 ("vfio/pci: Remove #ifdef iowrite64 and #ifdef
ioread64") inadvertently converted a conditional 8-byte rejection
into an unconditional one.

Originally, 'count == 8' was rejected only if iowrite64 was undefined
(#ifndef iowrite64). When iowrite64 became globally available via generic
fallbacks, this rejection became dead code, allowing 8-byte ioeventfds.
However, b44a06bd28f2 removed the #ifndef wrappers but left the nested
'if (count == 8) return -EINVAL;' intact, breaking all 8-byte
registrations.

Drop the unconditional check to restore 8-byte ioeventfd support,
matching the original intent.

Fixes: b44a06bd28f2 ("vfio/pci: Remove #ifdef iowrite64 and #ifdef ioread64")
Cc: stable@vger.kernel.org
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Link: https://lore.kernel.org/r/20260922040013.2188-1-lirongqing@baidu.com
Signed-off-by: Alex Williamson <alex@shazbot.org>
---
 drivers/vfio/pci/vfio_pci_rdwr.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c
index 7f14dd46de17a..df88480876815 100644
--- a/drivers/vfio/pci/vfio_pci_rdwr.c
+++ b/drivers/vfio/pci/vfio_pci_rdwr.c
@@ -423,9 +423,6 @@ int vfio_pci_ioeventfd(struct vfio_pci_core_device *vdev, loff_t offset,
 	      pos >= vdev->msix_offset + vdev->msix_size))
 		return -EINVAL;
 
-	if (count == 8)
-		return -EINVAL;
-
 	io = vfio_pci_core_get_iomap(vdev, bar);
 	if (IS_ERR(io))
 		return PTR_ERR(io);
-- 
2.53.0