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

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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>
This commit is contained in:
Fuad Tabba
2025-07-29 15:54:40 -07:00
committed by Paolo Bonzini
parent 68d1899387
commit d1e54dd08f
4 changed files with 9 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
arch/x86/include/asm/kvm_host.h
View File

@@ -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)

12
arch/x86/kvm/Kconfig
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@@ -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

9
include/linux/kvm_host.h
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@@ -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)

4
virt/kvm/kvm_main.c
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@@ -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;