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

Avi Kivity
2009-12-23T13:44:51Z

On 12/23/2009 03:37 PM, Marcelo Tosatti wrote:
>
>> 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.
>

You're right.

Well, qemu knows about cpuid.rdtscp, so we can add it to vmstate if it
is enabled. We should probably whitelist flags in qemu in the same way
we whitelist them in kvm.

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