KVM: x86: Enable KVM_GUEST_MEMFD for all 64-bit builds

Enable KVM_GUEST_MEMFD for all KVM x86 64-bit builds, i.e. for "default"
VM types when running on 64-bit KVM.  This will allow using guest_memfd
to back non-private memory for all VM shapes, by supporting mmap() on
guest_memfd.

Opportunistically clean up various conditionals that become tautologies
once x86 selects KVM_GUEST_MEMFD more broadly.  Specifically, because
SW protected VMs, SEV, and TDX are all 64-bit only, private memory no
longer needs to take explicit dependencies on KVM_GUEST_MEMFD, because
it is effectively a prerequisite.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20250729225455.670324-10-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: Fuad Tabba

arch/x86/include/asm/kvm_host.h

@@ -2276,10 +2276,8 @@ void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level,
 		       int tdp_max_root_level, int tdp_huge_page_level);
 
 
-#ifdef CONFIG_KVM_GUEST_MEMFD
+#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
 #define kvm_arch_has_private_mem(kvm) ((kvm)->arch.has_private_mem)
-#else
-#define kvm_arch_has_private_mem(kvm) false
 #endif
 
 #define kvm_arch_has_readonly_mem(kvm) (!(kvm)->arch.has_protected_state)

arch/x86/kvm/Kconfig

@@ -47,6 +47,7 @@ config KVM_X86
 	select KVM_GENERIC_HARDWARE_ENABLING
 	select KVM_GENERIC_PRE_FAULT_MEMORY
 	select KVM_WERROR if WERROR
+	select KVM_GUEST_MEMFD if X86_64
 
 config KVM
 	tristate "Kernel-based Virtual Machine (KVM) support"
@@ -79,16 +80,11 @@ config KVM_WERROR
 
 	  If in doubt, say "N".
 
-config KVM_X86_PRIVATE_MEM
-	select KVM_GENERIC_MEMORY_ATTRIBUTES
-	select KVM_GUEST_MEMFD
-	bool
-
 config KVM_SW_PROTECTED_VM
 	bool "Enable support for KVM software-protected VMs"
 	depends on EXPERT
 	depends on KVM_X86 && X86_64
-	select KVM_X86_PRIVATE_MEM
+	select KVM_GENERIC_MEMORY_ATTRIBUTES
 	help
 	  Enable support for KVM software-protected VMs.  Currently, software-
 	  protected VMs are purely a development and testing vehicle for
@@ -138,7 +134,7 @@ config KVM_INTEL_TDX
 	bool "Intel Trust Domain Extensions (TDX) support"
 	default y
 	depends on INTEL_TDX_HOST
-	select KVM_X86_PRIVATE_MEM
+	select KVM_GENERIC_MEMORY_ATTRIBUTES
 	select HAVE_KVM_ARCH_GMEM_POPULATE
 	help
 	  Provides support for launching Intel Trust Domain Extensions (TDX)
@@ -162,7 +158,7 @@ config KVM_AMD_SEV
 	depends on KVM_AMD && X86_64
 	depends on CRYPTO_DEV_SP_PSP && !(KVM_AMD=y && CRYPTO_DEV_CCP_DD=m)
 	select ARCH_HAS_CC_PLATFORM
-	select KVM_X86_PRIVATE_MEM
+	select KVM_GENERIC_MEMORY_ATTRIBUTES
 	select HAVE_KVM_ARCH_GMEM_PREPARE
 	select HAVE_KVM_ARCH_GMEM_INVALIDATE
 	select HAVE_KVM_ARCH_GMEM_POPULATE

include/linux/kvm_host.h

@@ -719,11 +719,7 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu)
 }
 #endif
 
-/*
- * Arch code must define kvm_arch_has_private_mem if support for guest_memfd is
- * enabled.
- */
-#if !defined(kvm_arch_has_private_mem) && !IS_ENABLED(CONFIG_KVM_GUEST_MEMFD)
+#ifndef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
 static inline bool kvm_arch_has_private_mem(struct kvm *kvm)
 {
 	return false;
@@ -2505,8 +2501,7 @@ bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
 
 static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
 {
-	return IS_ENABLED(CONFIG_KVM_GUEST_MEMFD) &&
-	       kvm_get_memory_attributes(kvm, gfn) & KVM_MEMORY_ATTRIBUTE_PRIVATE;
+	return kvm_get_memory_attributes(kvm, gfn) & KVM_MEMORY_ATTRIBUTE_PRIVATE;
 }
 #else
 static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)

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 (IS_ENABLED(CONFIG_KVM_GUEST_MEMFD))
 		valid_flags |= KVM_MEM_GUEST_MEMFD;
 
 	/* Dirty logging private memory is not currently supported. */
@@ -4917,7 +4917,7 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 #endif
 #ifdef CONFIG_KVM_GUEST_MEMFD
 	case KVM_CAP_GUEST_MEMFD:
-		return !kvm || kvm_arch_has_private_mem(kvm);
+		return 1;
 #endif
 	default:
 		break;