[PATCH v2] KVM: arm64: Fix circular locking dependency

[PATCH v2] KVM: arm64: Fix circular locking dependency

[Sebastian Ene]

The rule inside kvm enforces that the vcpu->mutex is taken *inside*
kvm->lock. The rule is violated by the pkvm_create_hyp_vm() which acquires
the kvm->lock while already holding the vcpu->mutex lock from
kvm_vcpu_ioctl(). Avoid the circular locking dependency altogether by
protecting the hyp vm handle with the config_lock, much like we already
do for other forms of VM-scoped data.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
Cc: stable@vger.kernel.org
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/pkvm.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
index 8350fb8fee0b..b7be96a53597 100644
--- a/arch/arm64/kvm/pkvm.c
+++ b/arch/arm64/kvm/pkvm.c
@@ -101,6 +101,17 @@ void __init kvm_hyp_reserve(void)
 		 hyp_mem_base);
 }
 
+static void __pkvm_destroy_hyp_vm(struct kvm *host_kvm)
+{
+	if (host_kvm->arch.pkvm.handle) {
+		WARN_ON(kvm_call_hyp_nvhe(__pkvm_teardown_vm,
+					  host_kvm->arch.pkvm.handle));
+	}
+
+	host_kvm->arch.pkvm.handle = 0;
+	free_hyp_memcache(&host_kvm->arch.pkvm.teardown_mc);
+}
+
 /*
  * Allocates and donates memory for hypervisor VM structs at EL2.
  *
@@ -181,7 +192,7 @@ static int __pkvm_create_hyp_vm(struct kvm *host_kvm)
 	return 0;
 
 destroy_vm:
-	pkvm_destroy_hyp_vm(host_kvm);
+	__pkvm_destroy_hyp_vm(host_kvm);
 	return ret;
 free_vm:
 	free_pages_exact(hyp_vm, hyp_vm_sz);
@@ -194,23 +205,19 @@ int pkvm_create_hyp_vm(struct kvm *host_kvm)
 {
 	int ret = 0;
 
-	mutex_lock(&host_kvm->lock);
+	mutex_lock(&host_kvm->arch.config_lock);
 	if (!host_kvm->arch.pkvm.handle)
 		ret = __pkvm_create_hyp_vm(host_kvm);
-	mutex_unlock(&host_kvm->lock);
+	mutex_unlock(&host_kvm->arch.config_lock);
 
 	return ret;
 }
 
 void pkvm_destroy_hyp_vm(struct kvm *host_kvm)
 {
-	if (host_kvm->arch.pkvm.handle) {
-		WARN_ON(kvm_call_hyp_nvhe(__pkvm_teardown_vm,
-					  host_kvm->arch.pkvm.handle));
-	}
-
-	host_kvm->arch.pkvm.handle = 0;
-	free_hyp_memcache(&host_kvm->arch.pkvm.teardown_mc);
+	mutex_lock(&host_kvm->arch.config_lock);
+	__pkvm_destroy_hyp_vm(host_kvm);
+	mutex_unlock(&host_kvm->arch.config_lock);
 }
 
 int pkvm_init_host_vm(struct kvm *host_kvm)
-- 
2.43.0.429.g432eaa2c6b-goog

Re: [PATCH v2] KVM: arm64: Fix circular locking dependency

[Marc Zyngier]

On Wed, 24 Jan 2024 09:10:28 +0000, Sebastian Ene wrote:
> The rule inside kvm enforces that the vcpu->mutex is taken *inside*
> kvm->lock. The rule is violated by the pkvm_create_hyp_vm() which acquires
> the kvm->lock while already holding the vcpu->mutex lock from
> kvm_vcpu_ioctl(). Avoid the circular locking dependency altogether by
> protecting the hyp vm handle with the config_lock, much like we already
> do for other forms of VM-scoped data.

Applied to fixes, thanks!

[1/1] KVM: arm64: Fix circular locking dependency
      commit: 10c02aad111df02088d1a81792a709f6a7eca6cc

Cheers,

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