Re: [PATCH 1/2] KVM: x86 emulator: don't update vcpu state if instruction is restarted.

Gleb Natapov
2010-08-01T08:28:17Z

On Sat, Jul 31, 2010 at 08:25:13PM +0300, Avi Kivity wrote:
> On 07/29/2010 03:11 PM, Gleb Natapov wrote:
> >No need to update vcpu state since instruction is in the middle of the
> >emulation.
> >
> >Signed-off-by: Gleb Natapov<gleb@redhat.com>
> >---
> > arch/x86/kvm/x86.c | 31 +++++++++++++------------------
> > 1 files changed, 13 insertions(+), 18 deletions(-)
> >
> >diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >index 76fbc32..7e5f075 100644
> >--- a/arch/x86/kvm/x86.c
> >+++ b/arch/x86/kvm/x86.c
> >@@ -4057,32 +4057,27 @@ restart:
> > return handle_emulation_failure(vcpu);
> > }
> >
> >- toggle_interruptibility(vcpu, vcpu->arch.emulate_ctxt.interruptibility);
> >- kvm_x86_ops->set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
> >- memcpy(vcpu->arch.regs, c->regs, sizeof c->regs);
> >- kvm_rip_write(vcpu, vcpu->arch.emulate_ctxt.eip);
> >+ r = EMULATE_DONE;
> >
> >- if (vcpu->arch.emulate_ctxt.exception>= 0) {
> >+ if (vcpu->arch.emulate_ctxt.exception>= 0)
> > inject_emulated_exception(vcpu);
> >- return EMULATE_DONE;
> >- }
> >-
> >- if (vcpu->arch.pio.count) {
> >+ else if (vcpu->arch.pio.count) {
> > if (!vcpu->arch.pio.in)
> > vcpu->arch.pio.count = 0;
> >- return EMULATE_DO_MMIO;
> >- }
> >-
> >- if (vcpu->mmio_needed) {
> >+ r = EMULATE_DO_MMIO;
> >+ } else if (vcpu->mmio_needed) {
> > if (vcpu->mmio_is_write)
> > vcpu->mmio_needed = 0;
> >- return EMULATE_DO_MMIO;
> >- }
> >-
> >- if (vcpu->arch.emulate_ctxt.restart)
> >+ r = EMULATE_DO_MMIO;
> >+ } else if (vcpu->arch.emulate_ctxt.restart)
> > goto restart;
> >
> >- return EMULATE_DONE;
> >+ toggle_interruptibility(vcpu, vcpu->arch.emulate_ctxt.interruptibility);
> >+ kvm_x86_ops->set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
> >+ memcpy(vcpu->arch.regs, c->regs, sizeof c->regs);
> >+ kvm_rip_write(vcpu, vcpu->arch.emulate_ctxt.eip);
> >+
> >+ return r;
> > }
> > EXPORT_SYMBOL_GPL(emulate_instruction);
> >
>
> What about kvm-tpr-opt.c? It uses rip after pio.
>
It uses rip _during_ pio. And pio emulation changes rip
only at the end of emulation.

> It's true that it usually doesn't go through the emulator.
>
> --
> I have a truly marvellous patch that fixes the bug which this
> signature is too narrow to contain.

--
Gleb.