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

Avi Kivity
2010-08-01T08:54:40Z

On 08/01/2010 11:28 AM, Gleb Natapov wrote:
> 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.

But non-emulated pio does a skip_emulated_instruction() immediately (or
so the code in kvm-tpr-opt.c assumes:

> static void vtpr_ioport_write(void *opaque, uint32_t addr, uint32_t val)
> {
> CPUState *env = cpu_single_env;
> uint32_t rip;
>
> cpu_synchronize_state(env);
>
> rip = env->eip - 2;
> write_byte_virt(env, rip, 0x66);
> write_byte_virt(env, rip + 1, 0x90);

)

--
error compiling committee.c: too many arguments to function