Re: [Xen-devel] [PATCH][XSA-126] xen: limit guest control of PCI command register

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

On Mon, Apr 20, 2015 at 04:32:12PM +0200, Michael S. Tsirkin wrote:
> On Mon, Apr 20, 2015 at 03:08:09PM +0100, Jan Beulich wrote:
> > >>> On 20.04.15 at 15:43, <mst@xxxxxxxxxx> wrote:
> > > On Mon, Apr 13, 2015 at 01:51:06PM +0100, Jan Beulich wrote:
> > >> >>> On 13.04.15 at 14:47, <mst@xxxxxxxxxx> wrote:
> > >> > Can you check device capabilities register, offset 0x4 within
> > >> > pci express capability structure?
> > >> > Bit 15 is 15 Role-Based Error Reporting.
> > >> > Is it set?
> > >> > 
> > >> > The spec says:
> > >> > 
> > >> >        15
> > >> >        On platforms where robust error handling and PC-compatible 
> > >> > Configuration 
> > >> > Space probing is
> > >> >        required, it is suggested that software or firmware have the 
> > >> > Unsupported 
> > >> > Request Reporting Enable
> > >> >        bit Set for Role-Based Error Reporting Functions, but clear for 
> > >> > 1.0a 
> > >> > Functions. Software or
> > >> >        firmware can distinguish the two classes of Functions by 
> > >> > examining the 
> > >> > Role-Based Error Reporting
> > >> >        bit in the Device Capabilities register.
> > >> 
> > >> Yes, that bit is set.
> > > 
> > > curiouser and curiouser.
> > > 
> > > So with functions that do support Role-Based Error Reporting, we have
> > > this:
> > > 
> > > 
> > >   With device Functions implementing Role-Based Error Reporting, setting 
> > > the 
> > > Unsupported Request
> > >   Reporting Enable bit will not interfere with PC-compatible 
> > > Configuration 
> > > Space probing, assuming
> > >   that the severity for UR is left at its default of non-fatal. However, 
> > > setting the Unsupported Request
> > >   Reporting Enable bit will enable the Function to report UR errors 97 
> > > detected with posted Requests,
> > >   helping avoid this case for potential silent data corruption.
> > 
> > I still don't see what the PC-compatible config space probing has to
> > do with our issue.
> 
> I'm not sure but I think it's listed here because it causes a ton of URs
> when device scan probes unimplemented functions.
> 
> > > did firmware reconfigure this device to report URs as fatal errors then?
> > 
> > No, the Unsupported Request Error Serverity flag is zero.
> > 
> > Jan
> 
> OK, that's the correct configuration, so how come the box crashes when
> there's a UR then?

Ping - any update on this?
Do we can chalk this up to hardware bugs on a specific box?

> -- 
> MST

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