diff mbox series

[v3] KVM: x86: inhibit APICv when KVM_GUESTDBG_BLOCKIRQ active

Message ID 20211103143929.15264-1-mlevitsk@redhat.com (mailing list archive)
State New, archived
Headers show
Series [v3] KVM: x86: inhibit APICv when KVM_GUESTDBG_BLOCKIRQ active | expand

Commit Message

Maxim Levitsky Nov. 3, 2021, 2:39 p.m. UTC
KVM_GUESTDBG_BLOCKIRQ relies on interrupts being injected using
standard kvm's inject_pending_event, and not via APICv/AVIC.

Since this is a debug feature, just inhibit APICv/AVIC while
KVM_GUESTDBG_BLOCKIRQ is in use on at least one vCPU.

Fixes: 61e5f69ef0837 ("KVM: x86: implement KVM_GUESTDBG_BLOCKIRQ")

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/svm/avic.c         |  3 ++-
 arch/x86/kvm/vmx/vmx.c          |  3 ++-
 arch/x86/kvm/x86.c              | 21 +++++++++++++++++++++
 4 files changed, 26 insertions(+), 2 deletions(-)

Comments

Sean Christopherson Nov. 4, 2021, 7:26 p.m. UTC | #1
On Wed, Nov 03, 2021, Maxim Levitsky wrote:
> KVM_GUESTDBG_BLOCKIRQ relies on interrupts being injected using
> standard kvm's inject_pending_event, and not via APICv/AVIC.
> 
> Since this is a debug feature, just inhibit APICv/AVIC while
> KVM_GUESTDBG_BLOCKIRQ is in use on at least one vCPU.

Very clever!

> Fixes: 61e5f69ef0837 ("KVM: x86: implement KVM_GUESTDBG_BLOCKIRQ")
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---

With the below nits resolved (tested on Intel w/ APICv):

Reviewed-and-tested-by: Sean Christopherson <seanjc@google.com>

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ac83d873d65b0..5d30cea58182e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10703,6 +10703,25 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
>  	return ret;
>  }
>  
> +static void kvm_arch_vcpu_guestdbg_update_apicv_inhibit(struct kvm *kvm)
> +{
> +	struct kvm_vcpu *vcpu = NULL;

vcpu doesn't need to be initialized.

> +	int i;

Nit, I'd prefer we use reverse fir tree when it's convenient, i.e.

	bool block_irq_used = false;
	struct kvm_vcpu *vcpu;
	int i;

> +	bool block_irq_used = false;
> +
> +	down_write(&kvm->arch.apicv_update_lock);
> +
> +	kvm_for_each_vcpu(i, vcpu, kvm) {
> +		if (vcpu->guest_debug & KVM_GUESTDBG_BLOCKIRQ) {
> +			block_irq_used = true;
> +			break;
> +		}
> +	}
> +	__kvm_request_apicv_update(kvm, !block_irq_used,
> +					       APICV_INHIBIT_REASON_BLOCKIRQ);

Heh, this indentation is still messed up, I think you need to change your

	if (r == -ENOCOFFEE)
		maxim_get_coffee();

to

	while (r == -ENOCOFFEE)
		r = maxim_get_coffee();

> +	up_write(&kvm->arch.apicv_update_lock);
> +}
> +
>  int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>  					struct kvm_guest_debug *dbg)
>  {
> @@ -10755,6 +10774,8 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>  
>  	static_call(kvm_x86_update_exception_bitmap)(vcpu);
>  
> +	kvm_arch_vcpu_guestdbg_update_apicv_inhibit(vcpu->kvm);
> +
>  	r = 0;
>  
>  out:
> -- 
> 2.26.3
>
Maxim Levitsky Nov. 8, 2021, 8:55 a.m. UTC | #2
On Thu, 2021-11-04 at 19:26 +0000, Sean Christopherson wrote:
> On Wed, Nov 03, 2021, Maxim Levitsky wrote:
> > KVM_GUESTDBG_BLOCKIRQ relies on interrupts being injected using
> > standard kvm's inject_pending_event, and not via APICv/AVIC.
> > 
> > Since this is a debug feature, just inhibit APICv/AVIC while
> > KVM_GUESTDBG_BLOCKIRQ is in use on at least one vCPU.
> 
> Very clever!

Thanks! It is now possible to enjoy this,
after we broke our back making APICv/AVIC inhibition actually work...

> 
> > Fixes: 61e5f69ef0837 ("KVM: x86: implement KVM_GUESTDBG_BLOCKIRQ")
> > 
> > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> > ---
> 
> With the below nits resolved (tested on Intel w/ APICv):
> 
> Reviewed-and-tested-by: Sean Christopherson <seanjc@google.com>
> 
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index ac83d873d65b0..5d30cea58182e 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -10703,6 +10703,25 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
> >  	return ret;
> >  }
> >  
> > +static void kvm_arch_vcpu_guestdbg_update_apicv_inhibit(struct kvm *kvm)
> > +{
> > +	struct kvm_vcpu *vcpu = NULL;
> 
> vcpu doesn't need to be initialized.
True, fixed in v4
> 
> > +	int i;
> 
> Nit, I'd prefer we use reverse fir tree when it's convenient, i.e.
Fixed in v4

> 
> 	bool block_irq_used = false;
> 	struct kvm_vcpu *vcpu;
> 	int i;
> 
> > +	bool block_irq_used = false;
> > +
> > +	down_write(&kvm->arch.apicv_update_lock);
> > +
> > +	kvm_for_each_vcpu(i, vcpu, kvm) {
> > +		if (vcpu->guest_debug & KVM_GUESTDBG_BLOCKIRQ) {
> > +			block_irq_used = true;
> > +			break;
> > +		}
> > +	}
> > +	__kvm_request_apicv_update(kvm, !block_irq_used,
> > +					       APICV_INHIBIT_REASON_BLOCKIRQ);
> 
> Heh, this indentation is still messed up, I think you need to change your
> 
> 	if (r == -ENOCOFFEE)
> 		maxim_get_coffee();
> 
> to
> 
> 	while (r == -ENOCOFFEE)
> 		r = maxim_get_coffee();

Yep :-)

> 
> > +	up_write(&kvm->arch.apicv_update_lock);
> > +}
> > +
> >  int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
> >  					struct kvm_guest_debug *dbg)
> >  {
> > @@ -10755,6 +10774,8 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
> >  
> >  	static_call(kvm_x86_update_exception_bitmap)(vcpu);
> >  
> > +	kvm_arch_vcpu_guestdbg_update_apicv_inhibit(vcpu->kvm);
> > +
> >  	r = 0;
> >  
> >  out:
> > -- 
> > 2.26.3
> > 

Thanks for the review,
	Best regards,
		Maxim Levitsky
diff mbox series

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 88fce6ab4bbd7..8f6e15b95a4d8 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1034,6 +1034,7 @@  struct kvm_x86_msr_filter {
 #define APICV_INHIBIT_REASON_IRQWIN     3
 #define APICV_INHIBIT_REASON_PIT_REINJ  4
 #define APICV_INHIBIT_REASON_X2APIC	5
+#define APICV_INHIBIT_REASON_BLOCKIRQ	6
 
 struct kvm_arch {
 	unsigned long n_used_mmu_pages;
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 8052d92069e01..affc0ea98d302 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -904,7 +904,8 @@  bool svm_check_apicv_inhibit_reasons(ulong bit)
 			  BIT(APICV_INHIBIT_REASON_NESTED) |
 			  BIT(APICV_INHIBIT_REASON_IRQWIN) |
 			  BIT(APICV_INHIBIT_REASON_PIT_REINJ) |
-			  BIT(APICV_INHIBIT_REASON_X2APIC);
+			  BIT(APICV_INHIBIT_REASON_X2APIC) |
+			  BIT(APICV_INHIBIT_REASON_BLOCKIRQ);
 
 	return supported & BIT(bit);
 }
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 71f54d85f104c..e4fc9ff7cd944 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7565,7 +7565,8 @@  static void hardware_unsetup(void)
 static bool vmx_check_apicv_inhibit_reasons(ulong bit)
 {
 	ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
-			  BIT(APICV_INHIBIT_REASON_HYPERV);
+			  BIT(APICV_INHIBIT_REASON_HYPERV) |
+			  BIT(APICV_INHIBIT_REASON_BLOCKIRQ);
 
 	return supported & BIT(bit);
 }
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ac83d873d65b0..5d30cea58182e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10703,6 +10703,25 @@  int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
 	return ret;
 }
 
+static void kvm_arch_vcpu_guestdbg_update_apicv_inhibit(struct kvm *kvm)
+{
+	struct kvm_vcpu *vcpu = NULL;
+	int i;
+	bool block_irq_used = false;
+
+	down_write(&kvm->arch.apicv_update_lock);
+
+	kvm_for_each_vcpu(i, vcpu, kvm) {
+		if (vcpu->guest_debug & KVM_GUESTDBG_BLOCKIRQ) {
+			block_irq_used = true;
+			break;
+		}
+	}
+	__kvm_request_apicv_update(kvm, !block_irq_used,
+					       APICV_INHIBIT_REASON_BLOCKIRQ);
+	up_write(&kvm->arch.apicv_update_lock);
+}
+
 int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 					struct kvm_guest_debug *dbg)
 {
@@ -10755,6 +10774,8 @@  int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 
 	static_call(kvm_x86_update_exception_bitmap)(vcpu);
 
+	kvm_arch_vcpu_guestdbg_update_apicv_inhibit(vcpu->kvm);
+
 	r = 0;
 
 out: