Re: [PATCH] Clear temporary interrupt blocking on halt in real mode

[Laurent Vivier <Laurent.Vivier@bull.net>]

Le dimanche 10 août 2008 à 11:36 +0300, Avi Kivity a écrit :
> Laurent Vivier wrote:
> > When "halt" is emulated, skip_emulated_instruction() is called and interruptibility state is cleared.
> > But when halt is emulated in real mode, skip_emulated_instruction() is not called and the interruptiblity state is not cleared.
> >
> > The following code, from gPXE, never exits from loop because interrupts are not delivered to increase %fs:(0x6c):
> >
> >         movl    %fs:(0x6c), %eax
> > 1:      pushf
> >         sti
> >         hlt
> >         popf
> >         cmpl    %fs:(0x6c), %eax
> >         je      1b
> >
> > This patch clears the interruptibility state when halt is emulated in real mode.
> >
> > Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
> > ---
> >  arch/x86/kvm/vmx.c |   10 ++++++++++
> >  1 files changed, 10 insertions(+), 0 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index c4510fe..82c4324 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -2329,7 +2329,17 @@ static int handle_exception(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> >  	    handle_rmode_exception(vcpu, intr_info & INTR_INFO_VECTOR_MASK,
> >  								error_code)) {
> >  		if (vcpu->arch.halt_request) {
> > +			u32 interruptibility;
> >  			vcpu->arch.halt_request = 0;
> > +			/*
> > +			 * We emulated an instruction, so temporary interrupt blocking
> > +			 * should be removed, if set.
> > +                         */
> > +			interruptibility = vmcs_read32(GUEST_INTERRUPTIBILITY_INFO);
> > +			if (interruptibility & 3)
> > +				vmcs_write32(GUEST_INTERRUPTIBILITY_INFO,
> > +					     interruptibility & ~3);
> > +			vcpu->arch.interrupt_window_open = 1;
> >  			return kvm_emulate_halt(vcpu);
> >  		}
> >  		return 1;
> >   
> 
> 
> Shouldn't interruptibility state be cleared if *any* instruction is 
> emulated?
> 
> (of course, an emulated instruction may update interruptibility state 
> itself, say sti).

I don't know what to do with that...

I think emulated instructions already clear interruptibility state via
skip_emulated_instruction().

The case of kvm_emulate_halt() and real mode is a special case.

Laurent
-- 
----------------- Laurent.Vivier@bull.net  ------------------
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