Sheng Yang wrote:
On Wednesday 08 October 2008 18:14:22 Avi Kivity wrote:
Sheng Yang wrote:
Separate msr_bitmap for each vcpu, prepared for guest PAT support.
Why is this necessary? True, it reduces the overhead of the guest
reading and writing the PAT MSRs, but is such access frequent?
I would think guests set the PAT once, and never change it later.
Yeah. In fact, I just think msr_bitmap for each vcpu would be done sooner or
later, so get it done here. And it's natural to go with GUEST_PAT. And Xen
use it for another purpose(DEBUGCTLMSR related, I haven't checked it through)
(Also svm.c in KVM use per-vcpu msr bitmap)
svm.c uses it for last branch record; I think these are also rarely
accessed from the guest.
And without that, a callback should be implement to hook MSR write and update
guest pat write for both vmx and svm, or we should update GUEST PAT every
vmentry according to the vcpu->pat. Either way seems not that natural with
GUEST_PAT support.
We need the callbacks (vmx_set_msr and vmx_get_msr, or did you mean
something else?) anyway for save/restore support.
However, if you think msr_bitmap for each vcpu is a waste, I'd like to add
callbacks.
I agree that we will likely need msr bitmap support one day; but let's
start without it as this way we test the pat msr callbacks.
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I have a truly marvellous patch that fixes the bug which this
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