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

On Wed, Apr 04, 2018 at 04:45:32PM +0100, Roger Pau Monné wrote:
>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

Yes, that's why we have this patch -- to workaround a hardware issue.

>device is it that places random registers in the same page as the PBA?

According to the commit [1], Mellanox MT27500 series, ConnectX-3 VF.
And, a generation of Intel's Omni-Path.


Could you help to give some comments? :).


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