diff mbox series

[v7,02/12] KVM: arm64: PMU: Set the default PMU for the guest before vCPU reset

Message ID 20231009230858.3444834-3-rananta@google.com (mailing list archive)
State New, archived
Headers show
Series KVM: arm64: PMU: Allow userspace to limit the number of PMCs on vCPU | expand

Commit Message

Raghavendra Rao Ananta Oct. 9, 2023, 11:08 p.m. UTC 
From: Reiji Watanabe <reijiw@google.com>

The following patches will use the number of counters information
from the arm_pmu and use this to set the PMCR.N for the guest
during vCPU reset. However, since the guest is not associated
with any arm_pmu until userspace configures the vPMU device
attributes, and a reset can happen before this event, assign a
default PMU to the guest just before doing the reset.

Signed-off-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
---
 arch/arm64/kvm/arm.c      | 20 ++++++++++++++++++++
 arch/arm64/kvm/pmu-emul.c | 12 ++----------
 include/kvm/arm_pmu.h     |  6 ++++++
 3 files changed, 28 insertions(+), 10 deletions(-)

Comments

Oliver Upton Oct. 10, 2023, 10:25 p.m. UTC | #1 
Hi Raghu,

On Mon, Oct 09, 2023 at 11:08:48PM +0000, Raghavendra Rao Ananta wrote:
> From: Reiji Watanabe <reijiw@google.com>
> 
> The following patches will use the number of counters information
> from the arm_pmu and use this to set the PMCR.N for the guest
> during vCPU reset. However, since the guest is not associated
> with any arm_pmu until userspace configures the vPMU device
> attributes, and a reset can happen before this event, assign a
> default PMU to the guest just before doing the reset.
> 
> Signed-off-by: Reiji Watanabe <reijiw@google.com>
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> ---
>  arch/arm64/kvm/arm.c      | 20 ++++++++++++++++++++
>  arch/arm64/kvm/pmu-emul.c | 12 ++----------
>  include/kvm/arm_pmu.h     |  6 ++++++
>  3 files changed, 28 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 78b0970eb8e6..708a53b70a7b 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -1313,6 +1313,23 @@ static bool kvm_vcpu_init_changed(struct kvm_vcpu *vcpu,
>  			     KVM_VCPU_MAX_FEATURES);
>  }
>  
> +static int kvm_vcpu_set_pmu(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm *kvm = vcpu->kvm;
> +
> +	if (!kvm_arm_support_pmu_v3())
> +		return -EINVAL;

This check is pointless; the vCPU feature flags have been sanitised at
this point, and a requirement of having PMUv3 is that this predicate is
true.

> +	/*
> +	 * When the vCPU has a PMU, but no PMU is set for the guest
> +	 * yet, set the default one.
> +	 */
> +	if (unlikely(!kvm->arch.arm_pmu))
> +		return kvm_arm_set_default_pmu(kvm);
> +
> +	return 0;
> +}
> +

Apologies, I believe I was unclear last time around as to what I was
wanting here. Let's call this thing kvm_setup_vcpu() such that we can
add other one-time setup activities to it in the future.

Something like:

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 96641e442039..4896a44108e0 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1265,19 +1265,17 @@ static bool kvm_vcpu_init_changed(struct kvm_vcpu *vcpu,
 			     KVM_VCPU_MAX_FEATURES);
 }
 
-static int kvm_vcpu_set_pmu(struct kvm_vcpu *vcpu)
+static int kvm_setup_vcpu(struct kvm_vcpu *vcpu)
 {
 	struct kvm *kvm = vcpu->kvm;
 
-	if (!kvm_arm_support_pmu_v3())
-		return -EINVAL;
-
 	/*
 	 * When the vCPU has a PMU, but no PMU is set for the guest
 	 * yet, set the default one.
 	 */
-	if (unlikely(!kvm->arch.arm_pmu))
-		return kvm_arm_set_default_pmu(kvm);
+	if (kvm_vcpu_has_pmu(vcpu) && !kvm->arch.arm_pmu &&
+	    kvm_arm_set_default_pmu(kvm))
+		return -EINVAL;
 
 	return 0;
 }
@@ -1297,7 +1295,8 @@ static int __kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
 
 	bitmap_copy(kvm->arch.vcpu_features, &features, KVM_VCPU_MAX_FEATURES);
 
-	if (kvm_vcpu_has_pmu(vcpu) && kvm_vcpu_set_pmu(vcpu))
+	ret = kvm_setup_vcpu(vcpu);
+	if (ret)
 		goto out_unlock;
 
 	/* Now we know what it is, we can reset it. */
Raghavendra Rao Ananta Oct. 13, 2023, 8:27 p.m. UTC | #2 
On Tue, Oct 10, 2023 at 3:25 PM Oliver Upton <oliver.upton@linux.dev> wrote:
>
> Hi Raghu,
>
> On Mon, Oct 09, 2023 at 11:08:48PM +0000, Raghavendra Rao Ananta wrote:
> > From: Reiji Watanabe <reijiw@google.com>
> >
> > The following patches will use the number of counters information
> > from the arm_pmu and use this to set the PMCR.N for the guest
> > during vCPU reset. However, since the guest is not associated
> > with any arm_pmu until userspace configures the vPMU device
> > attributes, and a reset can happen before this event, assign a
> > default PMU to the guest just before doing the reset.
> >
> > Signed-off-by: Reiji Watanabe <reijiw@google.com>
> > Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> > ---
> >  arch/arm64/kvm/arm.c      | 20 ++++++++++++++++++++
> >  arch/arm64/kvm/pmu-emul.c | 12 ++----------
> >  include/kvm/arm_pmu.h     |  6 ++++++
> >  3 files changed, 28 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index 78b0970eb8e6..708a53b70a7b 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -1313,6 +1313,23 @@ static bool kvm_vcpu_init_changed(struct kvm_vcpu *vcpu,
> >                            KVM_VCPU_MAX_FEATURES);
> >  }
> >
> > +static int kvm_vcpu_set_pmu(struct kvm_vcpu *vcpu)
> > +{
> > +     struct kvm *kvm = vcpu->kvm;
> > +
> > +     if (!kvm_arm_support_pmu_v3())
> > +             return -EINVAL;
>
> This check is pointless; the vCPU feature flags have been sanitised at
> this point, and a requirement of having PMUv3 is that this predicate is
> true.
>
Oh yes. I'll avoid this in v8.

> > +     /*
> > +      * When the vCPU has a PMU, but no PMU is set for the guest
> > +      * yet, set the default one.
> > +      */
> > +     if (unlikely(!kvm->arch.arm_pmu))
> > +             return kvm_arm_set_default_pmu(kvm);
> > +
> > +     return 0;
> > +}
> > +
>
> Apologies, I believe I was unclear last time around as to what I was
> wanting here. Let's call this thing kvm_setup_vcpu() such that we can
> add other one-time setup activities to it in the future.
>
> Something like:
>
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 96641e442039..4896a44108e0 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -1265,19 +1265,17 @@ static bool kvm_vcpu_init_changed(struct kvm_vcpu *vcpu,
>                              KVM_VCPU_MAX_FEATURES);
>  }
>
> -static int kvm_vcpu_set_pmu(struct kvm_vcpu *vcpu)
> +static int kvm_setup_vcpu(struct kvm_vcpu *vcpu)
>  {
>         struct kvm *kvm = vcpu->kvm;
>
> -       if (!kvm_arm_support_pmu_v3())
> -               return -EINVAL;
> -
>         /*
>          * When the vCPU has a PMU, but no PMU is set for the guest
>          * yet, set the default one.
>          */
> -       if (unlikely(!kvm->arch.arm_pmu))
> -               return kvm_arm_set_default_pmu(kvm);
> +       if (kvm_vcpu_has_pmu(vcpu) && !kvm->arch.arm_pmu &&
> +           kvm_arm_set_default_pmu(kvm))
> +               return -EINVAL;
>
>         return 0;
>  }
> @@ -1297,7 +1295,8 @@ static int __kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
>
>         bitmap_copy(kvm->arch.vcpu_features, &features, KVM_VCPU_MAX_FEATURES);
>
> -       if (kvm_vcpu_has_pmu(vcpu) && kvm_vcpu_set_pmu(vcpu))
> +       ret = kvm_setup_vcpu(vcpu);
> +       if (ret)
>                 goto out_unlock;
>
>         /* Now we know what it is, we can reset it. */
>
Introducing kvm_setup_vcpu() seems better than directly calling
kvm_vcpu_set_pmu(), which feels like it's crashing a party.

Thank you.
Raghavendra
> --
> Thanks,
> Oliver
diff mbox series

Patch

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 78b0970eb8e6..708a53b70a7b 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1313,6 +1313,23 @@  static bool kvm_vcpu_init_changed(struct kvm_vcpu *vcpu,
 			     KVM_VCPU_MAX_FEATURES);
 }
 
+static int kvm_vcpu_set_pmu(struct kvm_vcpu *vcpu)
+{
+	struct kvm *kvm = vcpu->kvm;
+
+	if (!kvm_arm_support_pmu_v3())
+		return -EINVAL;
+
+	/*
+	 * When the vCPU has a PMU, but no PMU is set for the guest
+	 * yet, set the default one.
+	 */
+	if (unlikely(!kvm->arch.arm_pmu))
+		return kvm_arm_set_default_pmu(kvm);
+
+	return 0;
+}
+
 static int __kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
 				 const struct kvm_vcpu_init *init)
 {
@@ -1328,6 +1345,9 @@  static int __kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
 
 	bitmap_copy(kvm->arch.vcpu_features, &features, KVM_VCPU_MAX_FEATURES);
 
+	if (kvm_vcpu_has_pmu(vcpu) && kvm_vcpu_set_pmu(vcpu))
+		goto out_unlock;
+
 	/* Now we know what it is, we can reset it. */
 	kvm_reset_vcpu(vcpu);
 
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index eb5dcb12dafe..cc30c246c010 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -717,8 +717,7 @@  static struct arm_pmu *kvm_pmu_probe_armpmu(void)
 	 * It is still necessary to get a valid cpu, though, to probe for the
 	 * default PMU instance as userspace is not required to specify a PMU
 	 * type. In order to uphold the preexisting behavior KVM selects the
-	 * PMU instance for the core where the first call to the
-	 * KVM_ARM_VCPU_PMU_V3_CTRL attribute group occurs. A dependent use case
+	 * PMU instance for the core during the vcpu reset. A dependent use case
 	 * would be a user with disdain of all things big.LITTLE that affines
 	 * the VMM to a particular cluster of cores.
 	 *
@@ -893,7 +892,7 @@  static void kvm_arm_set_pmu(struct kvm *kvm, struct arm_pmu *arm_pmu)
  * where vCPUs can be scheduled on any core but the guest
  * counters could stop working.
  */
-static int kvm_arm_set_default_pmu(struct kvm *kvm)
+int kvm_arm_set_default_pmu(struct kvm *kvm)
 {
 	struct arm_pmu *arm_pmu = kvm_pmu_probe_armpmu();
 
@@ -946,13 +945,6 @@  int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 	if (vcpu->arch.pmu.created)
 		return -EBUSY;
 
-	if (!kvm->arch.arm_pmu) {
-		int ret = kvm_arm_set_default_pmu(kvm);
-
-		if (ret)
-			return ret;
-	}
-
 	switch (attr->attr) {
 	case KVM_ARM_VCPU_PMU_V3_IRQ: {
 		int __user *uaddr = (int __user *)(long)attr->addr;
diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index 3546ebc469ad..858ed9ce828a 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h
@@ -101,6 +101,7 @@  void kvm_vcpu_pmu_resync_el0(void);
 })
 
 u8 kvm_arm_pmu_get_pmuver_limit(void);
+int kvm_arm_set_default_pmu(struct kvm *kvm);
 
 #else
 struct kvm_pmu {
@@ -174,6 +175,11 @@  static inline u8 kvm_arm_pmu_get_pmuver_limit(void)
 }
 static inline void kvm_vcpu_pmu_resync_el0(void) {}
 
+static inline int kvm_arm_set_default_pmu(struct kvm *kvm)
+{
+	return -ENODEV;
+}
+
 #endif
 
 #endif