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

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

[lirongqing]

From: Li RongQing <lirongqing@baidu.com>

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>
---
 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 7f14dd4..df88480 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);
-- 
2.9.4

Re: [PATCH] vfio/pci: Restore 8-byte ioeventfd support

[Alex Williamson]

On Tue, 22 Sep 2026 12:00:13 +0800
lirongqing <lirongqing@baidu.com> wrote:

> From: Li RongQing <lirongqing@baidu.com>
> 
> 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>
> ---
>  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 7f14dd4..df88480 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);

Applied to vfio next branch for v7.4.  Thanks!

Alex