Re: [Xen-devel] [PATCH v4 1/3] xen/pt: fix some pass-thru devices don't work across reboot

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.12.18 at 11:26, <roger.pau@xxxxxxxxxx> wrote:
> On Fri, Dec 21, 2018 at 03:13:50AM -0700, Jan Beulich wrote:
>> But then again I'm still not fully convinced that a hypervisor
>> change is the right course of action here in the first place. It
>> would be better if the hypervisor had to just verify that all
>> IRQ mappings are gone, or else fail the de-assignment of the
>> device.
> 
> The only component (except the hypervisor) that knows about such
> assignments is QEMU, and in the case of a QEMU crash the host would be
> left with a device that cannot be de-assigned, because the information
> about the PIRQ bindings in lost due to the QEMU crash.
> 
> IMO Xen needs to be capable of cleaning any bindings and mappings done
> by the toolstack or the device model in order to be able to correctly
> recover from a device model or toolstack crash.

But possibly with tool stack assistance: Rather than doing it (in a
potentially fragile way, as per my other comments) as an integral
part of deassign-device, it could be a separate domctl to be
issued first. Or otherwise failure here ought to lead to failure of
deassign-device, rather than (e.g.) an infinite loop.

Jan



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