Re: pci-assign terminates the guest upon pread() / pwrite() error?

[Etienne Martineau <etmartin101@gmail.com>]

On 09/20/2012 02:16 PM, Alex Williamson wrote:
> On Thu, 2012-09-20 at 13:27 -0400, Etienne Martineau wrote:
>> In hw/kvm/pci-assign.c a pread() error part of assigned_dev_pci_read()
>> result in a hw_error(). Similarly a pwrite() error part of
>> assigned_dev_pci_write() also result in a hw_error().
>>
>> Would there be a way to avoid terminating the guest for those cases? How
>> about we deassign the device upon error?
>
> By terminating the guest we contain the error vs allowing the guest to
> continue running with invalid data.  De-assigning the device is
> asynchronous and relies on guest involvement, so damage is potentially
> already done.  Is this a theoretical problem or do you actually have
> hardware that hits this?  Thanks,
>
> Alex
>

This problem is in the context of a Hot-pluggable device assigned to the 
guest. If the guest rd/wr the config space at the same time than the 
device is physically taken out then the guest will terminate with 
hw_error().

Because this limits the availability of the guest I think we should try 
to recover instead. I don't see what other damage can happen since 
guest's MMIO access to the stale device will go nowhere?

-Etienne