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

[Gleb Natapov <gleb@redhat.com>]

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.