On 7/29/2026 8:35 AM, Ackerley Tng via B4 Relay wrote:
From: Ackerley Tng <[email protected]>
Make gmem_in_place_conversion a module parameter so that userspace can
configure enable or disable the use of VM-level memory attributes. The
module parameter is only available if CONFIG_KVM_VM_MEMORY_ATTRIBUTES is
enabled.
To avoid inconsistencies in the way memory attributes are tracked in KVM
and guest_memfd, the vm_memory_attributes module_param is made
read-only (0444).
Since selecting CONFIG_KVM_VM_MEMORY_ATTRIBUTES disables in-place
conversion, actually make CONFIG_KVM_VM_MEMORY_ATTRIBUTES selectable. Make
the config only selectable for (CoCo) VM types that might use
vm_memory_attributes.
Since memory attributes are trackable in guest_memfd, the concept of having
private memory is no longer dependent on
CONFIG_KVM_VM_MEMORY_ATTRIBUTES. Define kvm_arch_has_private_mem() based on
platform config, so that having private memory is dependent on (CoCo) VM
type.
Signed-off-by: Sean Christopherson <[email protected]>
Reviewed-by: Fuad Tabba <[email protected]>
Tested-by: Shivank Garg <[email protected]>
[Define module_param only if CONFIG_KVM_VM_MEMORY_ATTRIBUTES is enabled]
Suggested-by: Xiaoyao Li <[email protected]>
Signed-off-by: Ackerley Tng <[email protected]>
---
arch/x86/include/asm/kvm_host.h | 4 +++-
arch/x86/kvm/Kconfig | 14 ++++++++++----
virt/kvm/guest_memfd.c | 2 ++
virt/kvm/kvm_main.c | 5 ++++-
4 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ceb2abf43b76f..766eb094eaae6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1849,7 +1849,9 @@ enum kvm_intr_type {
((vcpu) && (vcpu)->arch.handling_intr_from_guest && \
(!!in_nmi() == ((vcpu)->arch.handling_intr_from_guest ==
KVM_HANDLING_NMI)))
-#ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
+#if defined(CONFIG_KVM_SW_PROTECTED_VM) || \
+ defined(CONFIG_KVM_INTEL_TDX) || \
+ defined(CONFIG_KVM_AMD_SEV)
#define kvm_arch_has_private_mem(kvm) ((kvm)->arch.has_private_mem)
#endif
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index abb108886733a..2c3c22aeafa54 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -81,13 +81,21 @@ config KVM_WERROR
If in doubt, say "N".
config KVM_VM_MEMORY_ATTRIBUTES
- bool
+ bool "Enable per-VM PRIVATE vs. SHARED attributes (for CoCo VMs)"
+ depends on KVM_SW_PROTECTED_VM || KVM_INTEL_TDX || KVM_AMD_SEV
+ help
+ Enable support for tracking PRIVATE vs. SHARED memory using per-VM
+ memory attributes. Using per-VM attributes is deprecated in favor of
+ tracking PRIVATE state in guest_memfd. Select this if you need to run
+ CoCo VMs using a VMM that doesn't support guest_memfd memory
+ attributes.
+
+ If unsure, say N.
config KVM_SW_PROTECTED_VM
bool "Enable support for KVM software-protected VMs"
depends on EXPERT
depends on KVM_X86 && X86_64
- select KVM_VM_MEMORY_ATTRIBUTES
help
Enable support for KVM software-protected VMs. Currently, software-
protected VMs are purely a development and testing vehicle for
@@ -138,7 +146,6 @@ config KVM_INTEL_TDX
bool "Intel Trust Domain Extensions (TDX) support"
default y
depends on INTEL_TDX_HOST
- select KVM_VM_MEMORY_ATTRIBUTES
select HAVE_KVM_ARCH_GMEM_POPULATE
help
Provides support for launching Intel Trust Domain Extensions (TDX)
@@ -162,7 +169,6 @@ 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_VM_MEMORY_ATTRIBUTES
select HAVE_KVM_ARCH_GMEM_CONVERT
select HAVE_KVM_ARCH_GMEM_RECLAIM
select HAVE_KVM_ARCH_GMEM_INVALIDATE
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index ea2752989f8bd..df67a6188aa99 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -1137,10 +1137,12 @@ static bool kvm_range_is_private(struct file *file,
pgoff_t index,
{
struct inode *inode = file_inode(file);
+#ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
if (!gmem_in_place_conversion)
return kvm_range_has_vm_memory_attributes(kvm, gfn, gfn +
nr_pages,
KVM_MEMORY_ATTRIBUTE_PRIVATE,
KVM_MEMORY_ATTRIBUTE_PRIVATE);
+#endif
return kvm_gmem_range_has_attributes(inode, index, nr_pages,
KVM_MEMORY_ATTRIBUTE_PRIVATE);
With my suggestion[1] on patch 7, this diff block can be dropped.
[1]
https://lore.kernel.org/all/[email protected]/
The code looks good to me,
Reviewed-by: Xiaoyao Li <[email protected]>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e961cc297ba2a..eb9f433278d2f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -102,7 +102,10 @@ static bool __ro_after_init allow_unsafe_mappings;
module_param(allow_unsafe_mappings, bool, 0444);
#ifdef kvm_arch_has_private_mem
-bool __ro_after_init gmem_in_place_conversion = false;
+bool __ro_after_init gmem_in_place_conversion =
!IS_ENABLED(CONFIG_KVM_VM_MEMORY_ATTRIBUTES);
+#ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
+module_param(gmem_in_place_conversion, bool, 0444);
+#endif
EXPORT_SYMBOL_FOR_KVM_INTERNAL(gmem_in_place_conversion);
#endif
