Re: [PATCH v9 20/41] KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes

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
>   
>