Re: Question about XEN Hypervisor MSR capability exposion to VMs

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 31/10/15 02:53, Liuyingdong wrote:
> Hi All
>
> We encountered a blue screen problem when live migrate
> Win8.1/Win2012R2 64bit VM from V3 processor to non-V3
> processor sandbox, KVM does not has this problem.
>
> After looking into the MSR capabilities, we found XEN
> hypervisor exposed bit 39 and bit 18 to the VM, from
> Intel manual bit 39 refers to reserve bit and should
> not be set, bit 18 refers to MWAIT/MONITOR capability,
> from my understanding it should not exposed to the VM
> too.
> BTW, KVM does not expose bit 18/39 to the VM.
>
> Below is the boot message:
> (XEN) read msr: ecx=c0000083, msr_value=0xfffff80028ddf240
> (XEN) read msr: ecx=1a0, msr_value=0x4000801889
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> (XEN) write msr:msr=40000071, msr_value=0x10000000000082f
> (XEN) write msr:msr=40000070, msr_value=0x0
> (XEN) write msr:msr=40000071, msr_value=0x20000000000082f
> (XEN) write msr:msr=40000070, msr_value=0x0
> (XEN) read msr: ecx=17, msr_value=0x0
> (XEN) write msr:msr=8b, msr_value=0x0
> (XEN) read msr: ecx=8b, msr_value=0x2d00000000
>

Xen currently does not make any attempt to level MSRs (it is unfortunate
that this area has been overlooked).

I have also encountered windows BSODs for this - 0x109 Critical
Structure Corruption I am guessing?

I am currently working on fixes to CPUID levelling (as it is more
important than MSRs at the moment), but have plans to fix MSR levelling
after that.

~Andrew