[PATCH v11 12/18] KVM: x86: Enable guest_memfd shared memory for SW-protected VMs

[Fuad Tabba <tabba@google.com>]

Define the architecture-specific macro to enable shared memory support
in guest_memfd for relevant software-only VM types, specifically
KVM_X86_DEFAULT_VM and KVM_X86_SW_PROTECTED_VM.

Enable the KVM_GMEM_SHARED_MEM Kconfig option if KVM_SW_PROTECTED_VM is
enabled.

Co-developed-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
---
 arch/x86/include/asm/kvm_host.h | 10 ++++++++++
 arch/x86/kvm/Kconfig            |  1 +
 arch/x86/kvm/x86.c              |  3 ++-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 709cc2a7ba66..ce9ad4cd93c5 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2255,8 +2255,18 @@ void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level,
 
 #ifdef CONFIG_KVM_GMEM
 #define kvm_arch_supports_gmem(kvm) ((kvm)->arch.supports_gmem)
+
+/*
+ * CoCo VMs with hardware support that use guest_memfd only for backing private
+ * memory, e.g., TDX, cannot use guest_memfd with userspace mapping enabled.
+ */
+#define kvm_arch_supports_gmem_shared_mem(kvm)			\
+	(IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM) &&			\
+	 ((kvm)->arch.vm_type == KVM_X86_SW_PROTECTED_VM ||		\
+	  (kvm)->arch.vm_type == KVM_X86_DEFAULT_VM))
 #else
 #define kvm_arch_supports_gmem(kvm) false
+#define kvm_arch_supports_gmem_shared_mem(kvm) false
 #endif
 
 #define kvm_arch_has_readonly_mem(kvm) (!(kvm)->arch.has_protected_state)
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index b37258253543..fdf24b50af9d 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -47,6 +47,7 @@ config KVM_X86
 	select KVM_GENERIC_HARDWARE_ENABLING
 	select KVM_GENERIC_PRE_FAULT_MEMORY
 	select KVM_GENERIC_GMEM_POPULATE if KVM_SW_PROTECTED_VM
+	select KVM_GMEM_SHARED_MEM if KVM_SW_PROTECTED_VM
 	select KVM_WERROR if WERROR
 
 config KVM
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 035ced06b2dd..2a02f2457c42 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12718,7 +12718,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 		return -EINVAL;
 
 	kvm->arch.vm_type = type;
-	kvm->arch.supports_gmem = (type == KVM_X86_SW_PROTECTED_VM);
+	kvm->arch.supports_gmem =
+		type == KVM_X86_DEFAULT_VM || type == KVM_X86_SW_PROTECTED_VM;
 	/* Decided by the vendor code for other VM types.  */
 	kvm->arch.pre_fault_allowed =
 		type == KVM_X86_DEFAULT_VM || type == KVM_X86_SW_PROTECTED_VM;
-- 
2.49.0.1266.g31b7d2e469-goog