Re: [PATCH 0/6 v2] Add support for RDTSCP in VMX

Marcelo Tosatti
2009-12-23T13:37:51Z

On Tue, Dec 22, 2009 at 08:26:25PM +0200, Avi Kivity wrote:
> On 12/22/2009 07:26 PM, Marcelo Tosatti wrote:
>> On Sun, Dec 20, 2009 at 11:30:00AM +0200, Avi Kivity wrote:
>>
>>> On 12/18/2009 10:48 AM, Sheng Yang wrote:
>>>
>>> Applied all, thanks.
>>>
>> Need to save/restore MSR_TSC_AUX in qemu-kvm.
>>
>
> Should be automatic. After all, we expose all the MSR list, so qemu can
> read it and save everything there.

Hum, thinking a bit more about this (and reading Glauber's previous attempt) its not
entirely clear that using the list provided by KVM_GET_MSR_INDEX_LIST to automatically save/restore
is a good thing:

- The MSR must be saved in QEMU's CPUState representation, and its
likely that it won't exist prior to the addition there.

- What about savevm/loadvm versioning? Currently the QEMU migration
protocol is unable to deal with a new kernel that supports, for example,
MSR_TSC_AUX vs a kernel that does not (in case MSRs were automatically
saved), with the same qemu-kvm version.