On 30.10.2008, at 21:44, Anthony Liguori wrote:
Alexander Graf wrote:
On 30.10.2008, at 20:29, Avi Kivity wrote:
Alexander Graf wrote:
I don't see any benefit from actually exporting that MSR atm. KVM
does never read it and it'd just add additional overhead on every
userspace transition, as it'd need to be synced every time.
We only sync MSRs on save/restore.
Oh, really? Looks like I interpreted that code wrong :-).
Nevertheless, we don't use the hsave given by the guest OS, because
we can't trust it. So saving and restoring a non-used value sounds
pretty useless - unless you're migrating from KVM to Qemu. Is this
kind of migration (going to be) possible?
But what if the guest tries to reread the hsave value it wrote?
Couldn't that break a guest?
Yes, it could. I just haven't seen any VMM do that yet. But I agree -
it could be implemented, I just didn't deem it necessary for now.
Alex
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