[PATCH 1/8] KVM: arm64: Add generic check for system-supported vCPU features

Oliver Upton
2023-09-20T19:50:52Z

To date KVM has relied on kvm_reset_vcpu() failing when the vCPU feature
flags are unsupported by the system. This is a bit messy since
kvm_reset_vcpu() is called at runtime outside of the KVM_ARM_VCPU_INIT
ioctl when it is expected to succeed. Further complicating the matter is
that kvm_reset_vcpu() must tolerate be idemptotent to the config_lock,
as it isn't consistently called with the lock held.

Prepare to move feature compatibility checks out of kvm_reset_vcpu() with
a 'generic' check that compares the user-provided flags with a computed
maximum feature set for the system.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
arch/arm64/kvm/arm.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 4866b3f7b4ea..66f3720cdd3a 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1190,6 +1190,16 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level,
return -EINVAL;
}

+static unsigned long system_supported_vcpu_features(void)
+{
+ unsigned long features = KVM_VCPU_VALID_FEATURES;
+
+ if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1))
+ clear_bit(KVM_ARM_VCPU_EL1_32BIT, &features);
+
+ return features;
+}
+
static int kvm_vcpu_init_check_features(struct kvm_vcpu *vcpu,
const struct kvm_vcpu_init *init)
{
@@ -1204,12 +1214,12 @@ static int kvm_vcpu_init_check_features(struct kvm_vcpu *vcpu,
return -ENOENT;
}

+ if (features & ~system_supported_vcpu_features())
+ return -EINVAL;
+
if (!test_bit(KVM_ARM_VCPU_EL1_32BIT, &features))
return 0;

- if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1))
- return -EINVAL;
-
/* MTE is incompatible with AArch32 */
if (kvm_has_mte(vcpu->kvm))
return -EINVAL;
--
2.42.0.515.g380fc7ccd1-goog