KVM: arm64: Add generic check for system-supported vCPU features

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.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/r/20230920195036.1169791-2-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 4866b3f7b4ea3847d885e00cfac47a4d7abf9da3..8b5094343f84bbc18c47fd7f18aa6388e64b4beb 100644 (file)
--- 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_final_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;