Re: xen 4.15.5: msr_relaxed required for MSR 0x1a2

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

On Fri, Nov 17, 2023 at 09:18:39AM +0000, James Dingwall wrote:
> On Thu, Nov 16, 2023 at 04:32:47PM +0000, Andrew Cooper wrote:
> > On 16/11/2023 4:15 pm, James Dingwall wrote:
> > > Hi,
> > >
> > > Per the msr_relaxed documentation:
> > >
> > >    "If using this option is necessary to fix an issue, please report a 
> > > bug."
> > >
> > > After recently upgrading an environment from Xen 4.14.5 to Xen 4.15.5 we
> > > started experiencing a BSOD at boot with one of our Windows guests.  We 
> > > found
> > > that enabling `msr_relaxed = 1` in the guest configuration has resolved 
> > > the
> > > problem.  With a debug build of Xen and `hvm_debug=2048` on the command 
> > > line
> > > the following messages were caught as the BSOD happened:
> > >
> > > (XEN) [HVM:11.0] <vmx_msr_read_intercept> ecx=0x1a2
> > > (XEN) vmx.c:3298:d11v0 RDMSR 0x000001a2 unimplemented
> > > (XEN) d11v0 VIRIDIAN CRASH: 1e ffffffffc0000096 fffff80b8de81eb5 0 0
> > >
> > > I found that MSR 0x1a2 is MSR_TEMPERATURE_TARGET and from that this patch
> > > series from last month:
> > >
> > > https://patchwork.kernel.org/project/xen-devel/list/?series=796550
> > >
> > > Picking out just a small part of that fixes the problem for us. Although 
> > > the
> > > the patch is against 4.15.5 I think it would be relevant to more recent
> > > releases too.
> > 
> > Which version of Windows, and what hardware?
> > 
> > The Viridian Crash isn't about the RDMSR itself - it's presumably
> > collateral damage shortly thereafter.
> > 
> > Does filling in 0 for that MSR also resolve the issue?  It's model
> > specific and we absolutely cannot pass it through from real hardware
> > like that.
> > 
> 
> Hi Andrew,
> 
> Thanks for your response.  The guest is running Windows 10 and the crash
> happens in a proprietary hardware driver.

When you say proprietary you mean a custom driver made for your
use-case, or is this some vendor driver widely available?

Thanks, Roger.