[PATCH v14 11/21] KVM: x86/mmu: Allow NULL-able fault in kvm_max_private_mapping_level

[Fuad Tabba <tabba@google.com>]

From: Ackerley Tng <ackerleytng@google.com>

Refactor kvm_max_private_mapping_level() to accept a NULL kvm_page_fault
pointer and rename it to kvm_gmem_max_mapping_level().

The max_mapping_level x86 operation (previously private_max_mapping_level)
is designed to potentially be called without an active page fault, for
instance, when kvm_mmu_max_mapping_level() is determining the maximum
mapping level for a gfn proactively.

Allow NULL fault pointer: Modify kvm_max_private_mapping_level() to
safely handle a NULL fault argument. This aligns its interface with the
kvm_x86_ops.max_mapping_level operation it wraps, which can also be
called with NULL.

Rename function to kvm_gmem_max_mapping_level(): This reinforces that
the function's scope is for guest_memfd-backed memory, which can be
either private or non-private, removing any remaining "private"
connotation from its name.

Optimize max_level checks: Introduce a check in the caller to skip
querying for max_mapping_level if the current max_level is already
PG_LEVEL_4K, as no further reduction is possible.

Acked-by: David Hildenbrand <david@redhat.com>
Suggested-by: Sean Christoperson <seanjc@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
---
 arch/x86/kvm/mmu/mmu.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index bb925994cbc5..6bd28fda0fd3 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4467,17 +4467,13 @@ static inline u8 kvm_max_level_for_order(int order)
 	return PG_LEVEL_4K;
 }
 
-static u8 kvm_max_private_mapping_level(struct kvm *kvm,
-					struct kvm_page_fault *fault,
-					int gmem_order)
+static u8 kvm_gmem_max_mapping_level(struct kvm *kvm, int order,
+				     struct kvm_page_fault *fault)
 {
-	u8 max_level = fault->max_level;
 	u8 req_max_level;
+	u8 max_level;
 
-	if (max_level == PG_LEVEL_4K)
-		return PG_LEVEL_4K;
-
-	max_level = min(kvm_max_level_for_order(gmem_order), max_level);
+	max_level = kvm_max_level_for_order(order);
 	if (max_level == PG_LEVEL_4K)
 		return PG_LEVEL_4K;
 
@@ -4513,7 +4509,9 @@ static int kvm_mmu_faultin_pfn_private(struct kvm_vcpu *vcpu,
 	}
 
 	fault->map_writable = !(fault->slot->flags & KVM_MEM_READONLY);
-	fault->max_level = kvm_max_private_mapping_level(vcpu->kvm, fault, max_order);
+	if (fault->max_level >= PG_LEVEL_4K)
+		fault->max_level = kvm_gmem_max_mapping_level(vcpu->kvm,
+							      max_order, fault);
 
 	return RET_PF_CONTINUE;
 }
-- 
2.50.0.727.gbf7dc18ff4-goog