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Re: [PATCH] xen/privcmd: Only claim ioreqs matching an ioeventfd
- To: Koichiro Den <den@xxxxxxxxxxxxx>, Viresh Kumar <viresh.kumar@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Thu, 8 Oct 2026 12:37:02 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
- Delivery-date: Thu, 08 Oct 2026 10:37:08 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21.08.26 10:41, Koichiro Den wrote:
The ioeventfd handler shares its event channel with the userspace device
model. It must only claim requests that match a registered ioeventfd.
Other requests are left for userspace.
ioeventfd_interrupt() currently marks every MMIO write INPROCESS before
looking for a match. For an unmatched request it drops the lock and
restores READY. Userspace may see INPROCESS and skip it. Restoring READY
does not send another notification. If userspace handles the request at
the same time, the READY store may overwrite its state.
Find a matching ioeventfd before changing the request state.
The lock now protects only the ioeventfd list. Use explicit virt_*mb()
barriers for the ioreq shared with Xen.
Fixes: f0d7db7b3324 ("xen: privcmd: Add support for ioeventfd")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Juergen
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