[PATCH 6.18.y] vfio/pci: Restore 8-byte ioeventfd support

[Sasha Levin <sashal@kernel.org>]

From: Li RongQing <lirongqing@baidu.com>

[ Upstream commit b30b52c2fb82e6d38ee2845a4d85e8254b44f3d8 ]

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>
[ sashal: Adjusted context to retain vfio_pci_core_setup_barmap() instead of vfio_pci_core_get_iomap(). ]
Signed-off-by: Sasha Levin <sashal@kernel.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 25380b7dfe18a..8338708b99c1e 100644
--- a/drivers/vfio/pci/vfio_pci_rdwr.c
+++ b/drivers/vfio/pci/vfio_pci_rdwr.c
@@ -449,9 +449,6 @@ 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;
-
 	ret = vfio_pci_core_setup_barmap(vdev, bar);
 	if (ret)
 		return ret;
-- 
2.53.0