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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: 0c2c7c0692 ("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>
This commit is contained in:
Sean Christopherson 2022-06-13 21:42:37 +00:00 committed by Paolo Bonzini
parent 5bdae49fc2
commit e5380f6d75
1 changed files with 7 additions and 10 deletions
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17
arch/x86/kvm/svm/sev.c
View File

@ -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);
}