[PATCH v2 4/4] KVM: x86/mmu: Exit to userspace on make_mmu_pages_available() error

[Sean Christopherson <sean.j.christopherson@intel.com>]

Propagate any error returned by make_mmu_pages_available() out to
userspace instead of resuming the guest if the error occurs while
handling a page fault.  Now that zapping the oldest MMU pages skips
active roots, i.e. fails if and only if there are no zappable pages,
there is no chance for a false positive, i.e. no chance of returning a
spurious error to userspace.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/mmu/mmu.c         | 3 ++-
 arch/x86/kvm/mmu/paging_tmpl.h | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 4d40b21a67bd..82086d9eecb0 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4157,7 +4157,8 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 	spin_lock(&vcpu->kvm->mmu_lock);
 	if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
 		goto out_unlock;
-	if (make_mmu_pages_available(vcpu) < 0)
+	r = make_mmu_pages_available(vcpu);
+	if (r)
 		goto out_unlock;
 	r = __direct_map(vcpu, gpa, write, map_writable, max_level, pfn,
 			 prefault, is_tdp && lpage_disallowed);
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 58234bfaca07..a2db6971231d 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -865,7 +865,8 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
 		goto out_unlock;
 
 	kvm_mmu_audit(vcpu, AUDIT_PRE_PAGE_FAULT);
-	if (make_mmu_pages_available(vcpu) < 0)
+	r = make_mmu_pages_available(vcpu);
+	if (r)
 		goto out_unlock;
 	r = FNAME(fetch)(vcpu, addr, &walker, write_fault, max_level, pfn,
 			 map_writable, prefault, lpage_disallowed);
-- 
2.26.0