KVM: x86/mmu: Extend guest_memfd's max mapping level to shared mappings

Rework kvm_mmu_max_mapping_level() to consult guest_memfd for all mappings,
not just private mappings, so that hugepage support plays nice with the
upcoming support for backing non-private memory with guest_memfd.

In addition to getting the max order from guest_memfd for gmem-only
memslots, update TDX's hook to effectively ignore shared mappings, as TDX's
restrictions on page size only apply to Secure EPT mappings.  Do nothing
for SNP, as RMP restrictions apply to both private and shared memory.

Suggested-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-ID: <20250729225455.670324-16-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: sean-jc

arch/x86/include/asm/kvm_host.h

@@ -1922,7 +1922,7 @@ struct kvm_x86_ops {
 	void *(*alloc_apic_backing_page)(struct kvm_vcpu *vcpu);
 	int (*gmem_prepare)(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order);
 	void (*gmem_invalidate)(kvm_pfn_t start, kvm_pfn_t end);
-	int (*gmem_max_mapping_level)(struct kvm *kvm, kvm_pfn_t pfn);
+	int (*gmem_max_mapping_level)(struct kvm *kvm, kvm_pfn_t pfn, bool is_private);
 };
 
 struct kvm_x86_nested_ops {

arch/x86/kvm/mmu/mmu.c

@@ -3302,8 +3302,9 @@ static 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,
-					const struct kvm_memory_slot *slot, gfn_t gfn)
+static u8 kvm_gmem_max_mapping_level(struct kvm *kvm, struct kvm_page_fault *fault,
+				     const struct kvm_memory_slot *slot, gfn_t gfn,
+				     bool is_private)
 {
 	u8 max_level, coco_level;
 	kvm_pfn_t pfn;
@@ -3327,7 +3328,7 @@ static u8 kvm_max_private_mapping_level(struct kvm *kvm, struct kvm_page_fault *
 	 * restrictions.  A return of '0' means "no additional restrictions", to
 	 * allow for using an optional "ret0" static call.
 	 */
-	coco_level = kvm_x86_call(gmem_max_mapping_level)(kvm, pfn);
+	coco_level = kvm_x86_call(gmem_max_mapping_level)(kvm, pfn, is_private);
 	if (coco_level)
 		max_level = min(max_level, coco_level);
 
@@ -3361,8 +3362,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm, struct kvm_page_fault *fault,
 	if (max_level == PG_LEVEL_4K)
 		return PG_LEVEL_4K;
 
-	if (is_private)
-		host_level = kvm_max_private_mapping_level(kvm, fault, slot, gfn);
+	if (is_private || kvm_memslot_is_gmem_only(slot))
+		host_level = kvm_gmem_max_mapping_level(kvm, fault, slot, gfn,
+							is_private);
 	else
 		host_level = host_pfn_mapping_level(kvm, gfn, slot);
 	return min(host_level, max_level);

arch/x86/kvm/svm/sev.c

@@ -4943,7 +4943,7 @@ void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end)
 	}
 }
 
-int sev_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn)
+int sev_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, bool is_private)
 {
 	int level, rc;
 	bool assigned;

arch/x86/kvm/svm/svm.h

@@ -866,7 +866,7 @@ void sev_handle_rmp_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code);
 void sev_snp_init_protected_guest_state(struct kvm_vcpu *vcpu);
 int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order);
 void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end);
-int sev_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn);
+int sev_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, bool is_private);
 struct vmcb_save_area *sev_decrypt_vmsa(struct kvm_vcpu *vcpu);
 void sev_free_decrypted_vmsa(struct kvm_vcpu *vcpu, struct vmcb_save_area *vmsa);
 #else
@@ -895,7 +895,7 @@ static inline int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, in
 	return 0;
 }
 static inline void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end) {}
-static inline int sev_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn)
+static inline int sev_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, bool is_private)
 {
 	return 0;
 }

arch/x86/kvm/vmx/main.c

@@ -831,10 +831,11 @@ static int vt_vcpu_mem_enc_ioctl(struct kvm_vcpu *vcpu, void __user *argp)
 	return tdx_vcpu_ioctl(vcpu, argp);
 }
 
-static int vt_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn)
+static int vt_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn,
+				     bool is_private)
 {
 	if (is_td(kvm))
-		return tdx_gmem_max_mapping_level(kvm, pfn);
+		return tdx_gmem_max_mapping_level(kvm, pfn, is_private);
 
 	return 0;
 }

arch/x86/kvm/vmx/tdx.c

@@ -3318,8 +3318,11 @@ int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp)
 	return ret;
 }
 
-int tdx_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn)
+int tdx_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, bool is_private)
 {
+	if (!is_private)
+		return 0;
+
 	return PG_LEVEL_4K;
 }
 

arch/x86/kvm/vmx/x86_ops.h

@@ -153,7 +153,7 @@ int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp);
 void tdx_flush_tlb_current(struct kvm_vcpu *vcpu);
 void tdx_flush_tlb_all(struct kvm_vcpu *vcpu);
 void tdx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa, int root_level);
-int tdx_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn);
+int tdx_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, bool is_private);
 #endif
 
 #endif /* __KVM_X86_VMX_X86_OPS_H */