Re: [Xen-devel] [PATCH] xen: fix initialization of wallclock time for PVHVM on migration

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.06.13 at 14:01, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> On 06/11/2013 12:59 PM, Jan Beulich wrote:
>>>>> On 11.06.13 at 12:46, Roger Pau Monne <roger.pau@xxxxxxxxxx> wrote:
>>> The initial values of the wallclock time in the shared info page are
>>> set for PVHVM guests when the hypercall page is initialized, since the
>>> hypercall page is not reinitialized on resume, the hypervisor
>>> wallclock time is not properly set on resume.
>>>
>>> Fix it by forcing an update of the wallclock values when the shared
>>> info page is mapped.
>>
>> NACK - this is a guest side bug. After migration, a guest _has_ to
>> re-init the hypercall page, as it may have got migrated between
>> a VMX and an SVM machine, and the hypercall instructions are
>> different between them.
> 
> Does migrating from VMX to SVM actually work?

If you sufficiently feature-restrict both hosts, it should work. At
least it was made work years ago iirc (see the sysenter/syscall
emulation code in the x86 emulator - the only case where this
may be needed is when doing cross vendor migration).

Jan


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