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

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

On Thu, Apr 05, 2018 at 10:40:37AM +0100, George Dunlap wrote:
> On 04/05/2018 10:34 AM, 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.
> >>
> >> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
> >> ---
> >>  docs/misc/xen-command-line.markdown | 10 +++++++++
> >>  xen/arch/x86/msi.c                  |  7 ++++--
> >>  xen/drivers/passthrough/pci.c       | 45 
> >> +++++++++++++++++++++++++++++++++++--
> >>  xen/include/asm-x86/msi.h           |  1 +
> >>  4 files changed, 59 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/docs/misc/xen-command-line.markdown 
> >> b/docs/misc/xen-command-line.markdown
> >> index b353352..e382513 100644
> >> --- a/docs/misc/xen-command-line.markdown
> >> +++ b/docs/misc/xen-command-line.markdown
> >> @@ -1423,6 +1423,16 @@ Defaults to booting secondary processors.
> >>  
> >>  > Default: `on`
> >>  
> >> +### pba\_quirk
> > 
> > pba_write_allowed would be better, pba_quirk is too generic IMO.
> 
> 'quirk' was I think requested by Jan; and my understanding is that the
> word clearly indicates that the behavior in question is a workaround for
> hardware which is not compliant with the appropriate specification.  If
> you grep the source tree for 'quirk' you'll find a fairly large number.
> 
> pba_shared_quirk might be slightly more descriptive.

pba_write_quirk?

I just think it should be slightly more descriptive than pba_quirk in
case Xen has to add further PBA-related quirks in the future.

Roger.

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