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

Avi Kivity
2010-07-31T17:25:17Z

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'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.