On 7/23/2025 6:47 PM, Fuad Tabba wrote:
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@xxxxxxxxxx>
Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
It matches with my thought on v14 that gmem can be allowed for all x86
VM types[*]. Get rid of .supports_gmem and achieve it through
CONFIG_KVM_GUEST_MEMFD looks much cleaner!
[*]
https://lore.kernel.org/all/b5fe8f54-64df-4cfa-b86f-eed1cbddca7a@xxxxxxxxx/
---
arch/x86/include/asm/kvm_host.h | 4 +---
arch/x86/kvm/Kconfig | 12 ++++--------
include/linux/kvm_host.h | 9 ++-------
virt/kvm/kvm_main.c | 4 ++--
4 files changed, 9 insertions(+), 20 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7b0f2b3e492d..50366a1ca192 100644
--- 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 c763446d9b9f..4e43923656d0 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_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 56ea8c862cfd..4d1c44622056 100644
--- 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 aa86dfd757db..4f57cb92e109 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 (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;
