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

From: Chao Gao <chao.gao@intel.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Tim Deegan <tim@xen.org>, Ian Jackson <ian.jackson@eu.citrix.com>,
	xen-devel@lists.xen.org, Julien Grall <julien.grall@arm.com>,
	Jan Beulich <jbeulich@suse.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH] pci: a workaround for nonstandard PCI devices whose PBA shares
Date: Thu, 5 Apr 2018 00:20:37 +0800	[thread overview]
Message-ID: <20180404162035.GA93414@skl-4s-chao.sh.intel.com> (raw)
In-Reply-To: <20180404154532.nqdy4x3s2dvdsugn@MacBook-Pro-de-Roger.local>

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.

[1]:https://git.qemu.org/?p=qemu.git;a=commit;h=95239e162518dc6577164be3d9a789aba7f591a3

Could you help to give some comments? :).

Thanks
Chao

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