[PATCH v14 03/21] KVM: Introduce kvm_arch_supports_gmem()

[Fuad Tabba <tabba@google.com>]

Introduce kvm_arch_supports_gmem() to explicitly indicate whether an
architecture supports guest_memfd.

Previously, kvm_arch_has_private_mem() was used to check for guest_memfd
support. However, this conflated guest_memfd with "private" memory,
implying that guest_memfd was exclusively for CoCo VMs or other private
memory use cases.

With the expansion of guest_memfd to support non-private memory, such as
shared host mappings, it is necessary to decouple these concepts. The
new kvm_arch_supports_gmem() function provides a clear way to check for
guest_memfd support.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Shivank Garg <shivankg@amd.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Co-developed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
---
 arch/x86/include/asm/kvm_host.h |  4 +++-
 include/linux/kvm_host.h        | 11 +++++++++++
 virt/kvm/kvm_main.c             |  4 ++--
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index acb25f935d84..bde811b2d303 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2277,8 +2277,10 @@ void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level,
 
 #ifdef CONFIG_KVM_GMEM
 #define kvm_arch_has_private_mem(kvm) ((kvm)->arch.has_private_mem)
+#define kvm_arch_supports_gmem(kvm) kvm_arch_has_private_mem(kvm)
 #else
 #define kvm_arch_has_private_mem(kvm) false
+#define kvm_arch_supports_gmem(kvm) false
 #endif
 
 #define kvm_arch_has_readonly_mem(kvm) (!(kvm)->arch.has_protected_state)
@@ -2331,7 +2333,7 @@ enum {
 #define HF_SMM_INSIDE_NMI_MASK	(1 << 2)
 
 # define KVM_MAX_NR_ADDRESS_SPACES	2
-/* SMM is currently unsupported for guests with private memory. */
+/* SMM is currently unsupported for guests with guest_memfd private memory. */
 # define kvm_arch_nr_memslot_as_ids(kvm) (kvm_arch_has_private_mem(kvm) ? 1 : 2)
 # define kvm_arch_vcpu_memslots_id(vcpu) ((vcpu)->arch.hflags & HF_SMM_MASK ? 1 : 0)
 # define kvm_memslots_for_spte_role(kvm, role) __kvm_memslots(kvm, (role).smm)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 359baaae5e9f..ab1bde048034 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -729,6 +729,17 @@ static inline bool kvm_arch_has_private_mem(struct kvm *kvm)
 }
 #endif
 
+/*
+ * Arch code must define kvm_arch_supports_gmem if support for guest_memfd is
+ * enabled.
+ */
+#if !defined(kvm_arch_supports_gmem) && !IS_ENABLED(CONFIG_KVM_GMEM)
+static inline bool kvm_arch_supports_gmem(struct kvm *kvm)
+{
+	return false;
+}
+#endif
+
 #ifndef kvm_arch_has_readonly_mem
 static inline bool kvm_arch_has_readonly_mem(struct kvm *kvm)
 {
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d5f0ec2d321f..162e2a69cc49 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1588,7 +1588,7 @@ static int check_memory_region_flags(struct kvm *kvm,
 {
 	u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
 
-	if (kvm_arch_has_private_mem(kvm))
+	if (kvm_arch_supports_gmem(kvm))
 		valid_flags |= KVM_MEM_GUEST_MEMFD;
 
 	/* Dirty logging private memory is not currently supported. */
@@ -4915,7 +4915,7 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 #endif
 #ifdef CONFIG_KVM_GMEM
 	case KVM_CAP_GUEST_MEMFD:
-		return !kvm || kvm_arch_has_private_mem(kvm);
+		return !kvm || kvm_arch_supports_gmem(kvm);
 #endif
 	default:
 		break;
-- 
2.50.0.727.gbf7dc18ff4-goog