Alexander Graf wrote:
Neat trick. Have you looked at svm.c to see if we can cut out
extraneous instructions (or move them out of the gif=0 area)? Could
mean big savings.
Well for now I only emulate pre-vmrun and vmsave, because the emulator
breaks on lldt and set dr6 and ltr and ...
Yeah. We could move some of these out, and emulate the rest (ltr I
think is needed).
Move to the regular x86 emulator, so if we extend it with debug flag
support, privilege checking, etc, we get that for svm as well.
Do you seriously want to have a callback to svm specific code in the
x86 emulator?
That's what kvm_x86_ops is for. We already emulate vendor specific
instructions (vmcall and vmmcall).
I was thinking of doing that, but this way looked way cleaner to me. I
would actually rather use prefixes as hint on pattern matching.
So e.g. if we find a clgi instruction with some random prefix (or
somehow marked in other ways) we could just run a pattern that does
what the entry code would do. This way no emulation would be needed.
Smells like dynamic translation to me. I don't see how you could do
that generically -- it might work for one version of kvm, but not for
other hypervisors.
static int nested_svm_vmexit_real(struct vcpu_svm *svm, void *arg1,
void *arg2, void *opaque)
{
@@ -1551,6 +1600,9 @@ static int nested_svm_vmexit(struct vcpu_svm
*svm)
kvm_mmu_reset_context(&svm->vcpu);
kvm_mmu_load(&svm->vcpu);
+ /* KVM calls vmsave after vmrun, so let's run it now if we can */
+ nested_svm_emulate(svm, NULL);
+
Will also call stgi eventually, so it may make sense to loop here too.
See above - I did that, it broke, I tried to debug it for ~2 days and
just figured I'll leave it as is for now.
Certainly, we can leave it for later.
The current version gives _huge_ savings already.
Can you quantify?
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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