[RFC PATCH 1/5] KVM: x86/mmu: Log dirty GPAs only for the nested GPA walk

[Nikunj A Dadhania <nikunj@amd.com>]

Gate PML logging on the walk being the nested GPA walk, as only that walk
yields an L2 GPA.

No functional change intended, as the EPT template only backs the nested
GPA walk.  The upcoming nested SVM PML support runs this code for PTTYPE
64, which other walks reach too.

Assisted-by: LLM
Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
---
 arch/x86/kvm/mmu/paging_tmpl.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 8e350095508c..043d0ec02b27 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -235,7 +235,9 @@ static int FNAME(update_accessed_dirty_bits)(struct kvm_vcpu *vcpu,
 				!(pte & PT_GUEST_DIRTY_MASK)) {
 			trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte));
 #if PTTYPE == PTTYPE_EPT
-			if (kvm_nested_call(write_log_dirty)(vcpu, addr))
+			/* Only the nested GPA walk yields an L2 GPA to log. */
+			if (w == &vcpu->arch.ngpa_walk &&
+			    kvm_nested_call(write_log_dirty)(vcpu, addr))
 				return -EINVAL;
 #endif
 			pte |= PT_GUEST_DIRTY_MASK;
-- 
2.48.1