[PATCH v2] KVM: arm64: Fix hardware enable/disable flows for pKVM

[PATCH v2] KVM: arm64: Fix hardware enable/disable flows for pKVM

[Raghavendra Rao Ananta]

When running in protected mode, the hyp stub is disabled after pKVM is
initialized, meaning the host cannot enable/disable the hyp at
runtime. As such, kvm_arm_hardware_enabled is always 1 after
initialization, and kvm_arch_hardware_enable() never enables the vgic
maintenance irq or timer irqs.

Unconditionally enable/disable the vgic + timer irqs in the respective
calls, instead relying on the percpu bookkeeping in the generic code
to keep track of which cpus have the interrupts unmasked.

Fixes: 466d27e48d7c ("KVM: arm64: Simplify the CPUHP logic")
Reported-by: Oliver Upton <oliver.upton@linux.dev>
Suggested-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
---
 arch/arm64/kvm/arm.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index c2c14059f6a8..010ebfa69650 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1867,14 +1867,10 @@ static void _kvm_arch_hardware_enable(void *discard)
 
 int kvm_arch_hardware_enable(void)
 {
-	int was_enabled = __this_cpu_read(kvm_arm_hardware_enabled);
-
 	_kvm_arch_hardware_enable(NULL);
 
-	if (!was_enabled) {
-		kvm_vgic_cpu_up();
-		kvm_timer_cpu_up();
-	}
+	kvm_vgic_cpu_up();
+	kvm_timer_cpu_up();
 
 	return 0;
 }
@@ -1889,10 +1885,8 @@ static void _kvm_arch_hardware_disable(void *discard)
 
 void kvm_arch_hardware_disable(void)
 {
-	if (__this_cpu_read(kvm_arm_hardware_enabled)) {
-		kvm_timer_cpu_down();
-		kvm_vgic_cpu_down();
-	}
+	kvm_timer_cpu_down();
+	kvm_vgic_cpu_down();
 
 	if (!is_protected_kvm_enabled())
 		_kvm_arch_hardware_disable(NULL);
-- 
2.41.0.487.g6d72f3e995-goog

Re: [PATCH v2] KVM: arm64: Fix hardware enable/disable flows for pKVM

[Marc Zyngier]

On Wed, 19 Jul 2023 22:57:25 +0100,
Raghavendra Rao Ananta <rananta@google.com> wrote:
> 
> When running in protected mode, the hyp stub is disabled after pKVM is
> initialized, meaning the host cannot enable/disable the hyp at
> runtime. As such, kvm_arm_hardware_enabled is always 1 after
> initialization, and kvm_arch_hardware_enable() never enables the vgic
> maintenance irq or timer irqs.
> 
> Unconditionally enable/disable the vgic + timer irqs in the respective
> calls, instead relying on the percpu bookkeeping in the generic code
> to keep track of which cpus have the interrupts unmasked.
> 
> Fixes: 466d27e48d7c ("KVM: arm64: Simplify the CPUHP logic")
> Reported-by: Oliver Upton <oliver.upton@linux.dev>
> Suggested-by: Oliver Upton <oliver.upton@linux.dev>
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> ---
>  arch/arm64/kvm/arm.c | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index c2c14059f6a8..010ebfa69650 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -1867,14 +1867,10 @@ static void _kvm_arch_hardware_enable(void *discard)
>  
>  int kvm_arch_hardware_enable(void)
>  {
> -	int was_enabled = __this_cpu_read(kvm_arm_hardware_enabled);
> -
>  	_kvm_arch_hardware_enable(NULL);
>  
> -	if (!was_enabled) {
> -		kvm_vgic_cpu_up();
> -		kvm_timer_cpu_up();
> -	}
> +	kvm_vgic_cpu_up();
> +	kvm_timer_cpu_up();
>  
>  	return 0;
>  }
> @@ -1889,10 +1885,8 @@ static void _kvm_arch_hardware_disable(void *discard)
>  
>  void kvm_arch_hardware_disable(void)
>  {
> -	if (__this_cpu_read(kvm_arm_hardware_enabled)) {
> -		kvm_timer_cpu_down();
> -		kvm_vgic_cpu_down();
> -	}
> +	kvm_timer_cpu_down();
> +	kvm_vgic_cpu_down();
>  
>  	if (!is_protected_kvm_enabled())
>  		_kvm_arch_hardware_disable(NULL);

Note that this will likely conflict with the preemption disabling
patch that is on its way to upstream. Otherwise:

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH v2] KVM: arm64: Fix hardware enable/disable flows for pKVM

[Oliver Upton]

On Wed, 19 Jul 2023 21:57:25 +0000, Raghavendra Rao Ananta wrote:
> When running in protected mode, the hyp stub is disabled after pKVM is
> initialized, meaning the host cannot enable/disable the hyp at
> runtime. As such, kvm_arm_hardware_enabled is always 1 after
> initialization, and kvm_arch_hardware_enable() never enables the vgic
> maintenance irq or timer irqs.
> 
> Unconditionally enable/disable the vgic + timer irqs in the respective
> calls, instead relying on the percpu bookkeeping in the generic code
> to keep track of which cpus have the interrupts unmasked.
> 
> [...]

Applied to kvmarm/fixes, thanks!

[1/1] KVM: arm64: Fix hardware enable/disable flows for pKVM
      https://git.kernel.org/kvmarm/kvmarm/c/c718ca0e9940

--
Best,
Oliver