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>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7b0f2b3e492ddffb686a3f74e2b8c11334474420..50366a1ca192efa8a17e833ab21a9e3533734846 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/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)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index c763446d9b9f5f311c70dd7347a3ded583abbdeb..4e43923656d0e5d29e1e17d508a48a22990b7f3c 100644 (file)
--- 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_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

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 56ea8c862cfdfefed47079fc017280865e71e925..4d1c44622056c1179f9d0d1ec3f3c331162e56b7 100644 (file)
--- a/include/linux/kvm_host.h
+++ b/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)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index aa86dfd757db5785a2484e4b0cb1e7a6c55ec6cc..4f57cb92e10912c97ce7851e4ecdf7b67e9cf081 100644 (file)
--- 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 (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;