From e5380f6d7586ea3ef3a55d8cf19ceffacea31392 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Mon, 13 Jun 2022 21:42:37 +0000 Subject: [PATCH] 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: 0c2c7c069285 ("KVM: SEV: Mark nested locking of vcpu->lock") Reported-by: kernel test robot Cc: Peter Gonda Signed-off-by: Sean Christopherson Message-Id: <20220613214237.2538266-1-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm/sev.c | 17 +++++++---------- 1 file changed, 7 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 51fd985c..309bcdb 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -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); } -- 2.7.4