Re: [PATCH V1 02/16] xen/ioreq: Make x86's IOREQ feature common

[Jan Beulich <jbeulich@xxxxxxxx>]

On 30.09.2020 19:47, Julien Grall wrote:
> Regarding the fix itself, I am not sure what sort of synchronization we 
> can do. Are you suggesting to wait for the I/O to complete? If so, how 
> do we handle the case the IOREQ server died?

In simple cases retrying the entire request may be an option. However,
if the server died after some parts of a multi-part operation were
done already, I guess the resulting loss of state is bad enough to
warrant crashing the guest. This shouldn't be much different from e.g.
a device disappearing from a bare metal system - any partial I/O done
to/from it will leave the machine in an unpredictable state, which it
may be too difficult to recover from without rebooting. (Of course,
staying with this analogue, it may also be okay to simple consider
the operation "complete", leaving it to the guest to recover. The
main issue on the hypervisor side then would be to ensure we don't
expose any uninitialized [due to not having got written to] data to
the guest.)

Jan