KVM: x86: stop IO emulation cycle if instruction pointer is modified

KVM: x86: stop IO emulation cycle if instruction pointer is modified

[Marcelo Tosatti]

MMIO/PIO emulation should be interrupted if the system is restarted.
Otherwise in progress IO emulation continues at the instruction pointer,
even after vcpus' IP has been modified by KVM_SET_REGS.

Use IP change as an indicator to reset MMIO/PIO emulation state.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e8ba99c..9f7ce41 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6144,6 +6144,10 @@ int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 	kvm_register_write(vcpu, VCPU_REGS_R15, regs->r15);
 #endif
 
+	/* stop IO emulation cycle if RIP changes */
+	if (kvm_rip_read(vcpu) != regs->rip)
+		vcpu->arch.complete_userspace_io = NULL;
+
 	kvm_rip_write(vcpu, regs->rip);
 	kvm_set_rflags(vcpu, regs->rflags);
 

Re: KVM: x86: stop IO emulation cycle if instruction pointer is modified

[Gleb Natapov]

On Fri, Jul 05, 2013 at 04:16:55PM -0300, Marcelo Tosatti wrote:
> 
> MMIO/PIO emulation should be interrupted if the system is restarted.
> Otherwise in progress IO emulation continues at the instruction pointer,
> even after vcpus' IP has been modified by KVM_SET_REGS.
> 
> Use IP change as an indicator to reset MMIO/PIO emulation state.
> 
Userspace has to return to the kernel to complete pending IO operation.
This is documented in Documentation/virtual/kvm/api.txt. If this is not
what program does it is a bug. What userspace you see the problem with?

> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e8ba99c..9f7ce41 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6144,6 +6144,10 @@ int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
>  	kvm_register_write(vcpu, VCPU_REGS_R15, regs->r15);
>  #endif
>  
> +	/* stop IO emulation cycle if RIP changes */
> +	if (kvm_rip_read(vcpu) != regs->rip)
> +		vcpu->arch.complete_userspace_io = NULL;
> +
>  	kvm_rip_write(vcpu, regs->rip);
>  	kvm_set_rflags(vcpu, regs->rflags);
>  

--
			Gleb.

Re: KVM: x86: stop IO emulation cycle if instruction pointer is modified

[Marcelo Tosatti]

On Sat, Jul 06, 2013 at 10:41:12AM +0300, Gleb Natapov wrote:
> On Fri, Jul 05, 2013 at 04:16:55PM -0300, Marcelo Tosatti wrote:
> > 
> > MMIO/PIO emulation should be interrupted if the system is restarted.
> > Otherwise in progress IO emulation continues at the instruction pointer,
> > even after vcpus' IP has been modified by KVM_SET_REGS.
> > 
> > Use IP change as an indicator to reset MMIO/PIO emulation state.
> > 
> Userspace has to return to the kernel to complete pending IO operation.
> This is documented in Documentation/virtual/kvm/api.txt. If this is not
> what program does it is a bug. What userspace you see the problem with?

You're right, this patch should not be necessary.