Re: [PATCH] KVM: x86: Mask DR7 correctly on task-switch while debugging

[Paolo Bonzini <pbonzini@redhat.com>]

On 19/04/2015 14:18, Nadav Amit wrote:
> If the host sets hardware breakpoints to debug the guest, and a task-switch
> occurs in the guest, the architectural DR7 will not be updated. The effective
> DR7 would be updated instead.
> 
> This fix uses the standard DR setting mechanism instead of the one that was
> previously used. As a bonus, the update of DR7 will now be effective for AMD as
> well.

Is there a reason not to do it in emulate.c instead?

Paolo

> Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
> ---
>  arch/x86/kvm/vmx.c | 3 ---
>  arch/x86/kvm/x86.c | 3 +++
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index f7a0a7f..8f731c0 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5703,9 +5703,6 @@ static int handle_task_switch(struct kvm_vcpu *vcpu)
>  		return 0;
>  	}
>  
> -	/* clear all local breakpoint enable flags */
> -	vmcs_writel(GUEST_DR7, vmcs_readl(GUEST_DR7) & ~0x155);
> -
>  	/*
>  	 * TODO: What about debug traps on tss switch?
>  	 *       Are we supposed to inject them and update dr6?
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 2046be4..a170c35 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6816,6 +6816,9 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int idt_index,
>  
>  	kvm_rip_write(vcpu, ctxt->eip);
>  	kvm_set_rflags(vcpu, ctxt->eflags);
> +	ret = __kvm_set_dr(vcpu, 7, vcpu->arch.dr7 & ~(DR_LOCAL_ENABLE_MASK |
> +						       DR_LOCAL_SLOWDOWN));
> +	WARN_ON(ret != 0);
>  	kvm_make_request(KVM_REQ_EVENT, vcpu);
>  	return EMULATE_DONE;
>  }
>