Re: [PATCH] xen-hvm: Avoid livelock while handling buffered ioreqs

["Durrant, Paul" <xadimgnik@gmail.com>]

On 04/04/2024 15:08, Ross Lagerwall wrote:
> A malicious or buggy guest may generated buffered ioreqs faster than
> QEMU can process them in handle_buffered_iopage(). The result is a
> livelock - QEMU continuously processes ioreqs on the main thread without
> iterating through the main loop which prevents handling other events,
> processing timers, etc. Without QEMU handling other events, it often
> results in the guest becoming unsable and makes it difficult to stop the
> source of buffered ioreqs.
> 
> To avoid this, if we process a full page of buffered ioreqs, stop and
> reschedule an immediate timer to continue processing them. This lets
> QEMU go back to the main loop and catch up.
> 

Do PV backends potentially cause the same scheduling issue (if not using 
io threads)?

> Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
> ---
>   hw/xen/xen-hvm-common.c | 26 +++++++++++++++++---------
>   1 file changed, 17 insertions(+), 9 deletions(-)
> 

Reviewed-by: Paul Durrant <paul@xen.org>