Re: [Xen-devel] [PATCH] pci: a workaround for nonstandard PCI devices whose PBA shares

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Apr 04, 2018 at 11:29:39PM +0800, Chao Gao wrote:
> ... the same page with other registers which are not relevant to MSI-X. Xen
> marks pages where PBA resides as read-only. When assigning such devices to
> guest, device driver writes MSI-X irrelevant registers on those pages would
> lead to an EPT violation and the guest is destroyed because no handler is
> registered for those address range. In order to make guest capable to use such
> kind of devices, trapping very frequent write accesses is not a good idea for
> it would significantly impact the performance.
> 
> This patch provides a workaround with caveat. Specifically, an option is
> introduced to specify a list of devices. For those devices, Xen doesn't
> control the access right to pages where PBA resides. Hence, guest device
> driver is able to write those pages and functions well. Note that adding an
> untrusted device to this option may endanger security of the entire system.

This is a clear violation of the MSI-X spec. Out of curiosity, which
device is it that places random registers in the same page as the PBA?

Thanks, Roger.

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