[PATCH 2/4] KVM: SEV: Drop page refcount early during RMP fault handling

[Ackerley Tng]

When handling an RMP fault, KVM retrieves the PFN for a private GPA from
guest_memfd. The page reference taken during PFN lookup is not needed for
the remainder of the handler, as checking the RMP entry, splitting the
2MB page via PSMASH, and zapping shadow page tables only operate on PFNs.

Drop the page reference immediately after retrieving the PFN instead of
holding it across the entire handler.

A later patch will follow up with completely not returning refcounted pages
from kvm_gmem_get_pfn().

No functional change intended.

Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
 arch/x86/kvm/svm/sev.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index b2738362a928b..19c31fa944e34 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -5036,12 +5036,13 @@ void sev_handle_rmp_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code)
 				    gpa);
 		return;
 	}
+	kvm_release_page_unused(page);
 
 	ret = snp_lookup_rmpentry(pfn, &assigned, &rmp_level);
 	if (ret || !assigned) {
 		pr_warn_ratelimited("SEV: Unexpected RMP fault, no assigned RMP entry found for GPA 0x%llx PFN 0x%llx error %d\n",
 				    gpa, pfn, ret);
-		goto out_no_trace;
+		return;
 	}
 
 	/*
@@ -5088,8 +5089,6 @@ void sev_handle_rmp_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code)
 	kvm_zap_gfn_range(kvm, gfn, gfn + PTRS_PER_PMD);
 out:
 	trace_kvm_rmp_fault(vcpu, gpa, pfn, error_code, rmp_level, ret);
-out_no_trace:
-	kvm_release_page_unused(page);
 }
 
 static bool is_pfn_range_shared(kvm_pfn_t start, kvm_pfn_t end)

-- 
2.55.0.699.gb54405d56f-goog