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