RE: [Xen-devel] AMD crash on restore. bug in MTRR restore.4.0.2-rc2-pre

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 27.01.11 at 04:49, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:
> By saving the sysenter msrs in my PV drivers before the suspend
> hypercall and restoring them after, save/restore now works fine.
> 
> Does nobody else see a save/restore failure on AMD as a blocker to
> 4.0.2? It it something particular to my exact AMD CPU and OS (Windows
> 2008 x32)?

The 32-bit-ness of your Windows may matter: Looking at
xen/arch/hvm/svm/svm.c, I cannot see how
v->arch.hvm_svm.guest_sysenter_* would ever get set
in this case (given that the intercept for the respective MSRs
gets disabled in svm_update_guest_efer()), yet
svm_vmcb_save() reads this field unconditionally, whereas I
would think v->arch.hvm_svm.vmcb->sysenter_* should be
read/written in that case.

That code seems to go back to c/s 19856, fixing a boot
problem introduced in c/s 19648, which is the one that
removed the reads of the VMCB fields. Christoph?

Jan

>> -----Original Message-----
>> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-
>> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of James Harper
>> Sent: Thursday, 27 January 2011 13:32
>> To: xen-devel@xxxxxxxxxxxxxxxxxxx 
>> Cc: Tim Deegan
>> Subject: RE: [Xen-devel] AMD crash on restore. bug in MTRR
> restore.4.0.2-rc2-
>> pre
>> 
>> Additionally, WinDbg tells me that MSR's 175, and 176 are wiped out by
>> save/restore:
>> 
>> immediately before suspend
>> kd> rdmsr 174
>> msr[174] = 00000000`00000008
>> kd> rdmsr 175
>> msr[175] = 00000000`8039e000
>> kd> rdmsr 176
>> msr[176] = 00000000`816a4950
>> 
>> immediately after restore
>> kd> rdmsr 174
>> msr[174] = 00000000`00000000
>> kd> rdmsr 175
>> msr[175] = 00000000`00000000
>> kd> rdmsr 176
>> msr[176] = 00000000`00000000
>> 
>> although you're never too sure with WinDbg...
>> 
>> James



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