Commit e5380f6d authored Jun 13, 2022 by Sean Christopherson Committed by Paolo Bonzini Jun 15, 2022

KVM: SVM: Hide SEV migration lockdep goo behind CONFIG_PROVE_LOCKING

Wrap the manipulation of @role and the manual mutex_{release,acquire}()
invocations in CONFIG_PROVE_LOCKING=y to squash a clang-15 warning. When
building with -Wunused-but-set-parameter and CONFIG_DEBUG_LOCK_ALLOC=n,
clang-15 seees there's no usage of @role in mutex_lock_killable_nested()
and yells. PROVE_LOCKING selects DEBUG_LOCK_ALLOC, and the only reason
KVM manipulates @role is to make PROVE_LOCKING happy.

To avoid true ugliness, use "i" and "j" to detect the first pass in the
loops; the "idx" field that's used by kvm_for_each_vcpu() is guaranteed
to be '0' on the first pass as it's simply the first entry in the vCPUs
XArray, which is fully KVM controlled. kvm_for_each_vcpu() passes '0'
for xa_for_each_range()'s "start", and xa_for_each_range() will not enter
the loop if there's no entry at '0'.

Fixes: 0c2c7c06 ("KVM: SEV: Mark nested locking of vcpu->lock")
Reported-by: kernel test robot <lkp@intel.com>
Cc: Peter Gonda <pgonda@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220613214237.2538266-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 5bdae49f

arch/x86/kvm/svm/sev.c

+7 −10

Original line number	Diff line number	Diff line
		@@ -1606,38 +1606,35 @@ static int sev_lock_vcpus_for_migration(struct kvm *kvm,
		{
		struct kvm_vcpu *vcpu;
		unsigned long i, j;
		bool first = true;

		kvm_for_each_vcpu(i, vcpu, kvm) {
		if (mutex_lock_killable_nested(&vcpu->mutex, role))
		goto out_unlock;

		if (first) {
		#ifdef CONFIG_PROVE_LOCKING
		if (!i)
		/*
		* Reset the role to one that avoids colliding with
		* the role used for the first vcpu mutex.
		*/
		role = SEV_NR_MIGRATION_ROLES;
		first = false;
		} else {
		else
		mutex_release(&vcpu->mutex.dep_map, _THIS_IP_);
		}
		#endif
		}

		return 0;

		out_unlock:

		first = true;
		kvm_for_each_vcpu(j, vcpu, kvm) {
		if (i == j)
		break;

		if (first)
		first = false;
		else
		#ifdef CONFIG_PROVE_LOCKING
		if (j)
		mutex_acquire(&vcpu->mutex.dep_map, role, 0, _THIS_IP_);

		#endif

		mutex_unlock(&vcpu->mutex);
		}