[PATCH v4 4/5] KVM: SEV: Drop page refcount early in VMSA reload

[Ackerley Tng]

When reloading the guest VMSA for an SEV-SNP vCPU, KVM retrieves the PFN
from guest_memfd.

Drop the page reference immediately after retrieving the PFN instead of
holding it across MMU lock acquisition in preparation for a follow-up patch
to stop returning page pointers from guest_memfd PFN lookups.

This is safe because the page's validity and presence are governed by KVM's
MMU invalidation protocol rather than the page reference.

No functional change intended.

Reviewed-by: Michael Roth <michael.roth@xxxxxxx>
Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
 arch/x86/kvm/svm/sev.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index f9dce8acac8eb..f094b19226b92 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -4078,6 +4078,7 @@ static void __sev_snp_reload_vmsa(struct kvm_vcpu *vcpu, gpa_t gpa)
 	 */
 	if (kvm_gmem_get_pfn(vcpu->kvm, slot, gfn, &pfn, &page, NULL))
 		return;
+	kvm_release_page_clean(page);
 
 	read_lock(&kvm->mmu_lock);
 	/*
@@ -4092,8 +4093,6 @@ static void __sev_snp_reload_vmsa(struct kvm_vcpu *vcpu, gpa_t gpa)
 	else
 		svm->vmcb->control.vmsa_pa = pfn_to_hpa(pfn);
 	read_unlock(&kvm->mmu_lock);
-
-	kvm_release_page_clean(page);
 }
 
 /*

-- 
2.55.0.887.g758fc8c411-goog