Re: [PATCH v10 04/41] KVM: Enumerate support for PRIVATE memory iff kvm_arch_has_private_mem is defined

On 8/8/2026 5:52 AM, Ackerley Tng via B4 Relay wrote:
> From: Sean Christopherson <[email protected]>
> 
> Explicitly guard reporting support for KVM_MEMORY_ATTRIBUTE_PRIVATE based
> on kvm_arch_has_private_mem being #defined in anticipation of tracking
> PRIVATE vs. SHARED state per-guest_memfd, not per-VM (to allow in-place
> conversion).
> 
> guest_memfd support for memory attributes is expected to be unconditional
> to avoid yet more macros (all architectures that support guest_memfd are
> expected to use per-gmem attributes at some point), at which point
> enumerating support KVM_MEMORY_ATTRIBUTE_PRIVATE based solely on memory
> attributes being supported by KVM at-large would result in a system-scope
> check (NULL @kvm) over-reporting support on arm64.
> 
> Give architectures full control over overriding the default definition of
> kvm_arch_has_private_mem() by removing the coupling with
> CONFIG_KVM_VM_MEMORY_ATTRIBUTES.
> 
> In a later patch, kvm_arch_has_private_mem() will be defined based on
> whether architectural features are compiled in, and made orthogonal to
> CONFIG_KVM_VM_MEMORY_ATTRIBUTES.
> 
> Signed-off-by: Sean Christopherson <[email protected]>
> Reviewed-by: Fuad Tabba <[email protected]>
> Reviewed-by: Binbin Wu <[email protected]>
> Tested-by: Shivank Garg <[email protected]>
> Signed-off-by: Ackerley Tng <[email protected]>

Reviewed-by: Xiaoyao Li <[email protected]>

> ---
>   include/linux/kvm_host.h | 2 +-
>   virt/kvm/kvm_main.c      | 2 ++
>   2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 3e86cdd00e59b..e3666d0b40b74 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -722,7 +722,7 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu *vcpu)
>   }
>   #endif
>   
> -#ifndef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
> +#ifndef kvm_arch_has_private_mem
>   static inline bool kvm_arch_has_private_mem(struct kvm *kvm)
>   {
>   	return false;
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e3a77d1e6d8ae..560ff05e95959 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2422,8 +2422,10 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
>   #ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
>   static u64 kvm_supported_mem_attributes(struct kvm *kvm)
>   {
> +#ifdef kvm_arch_has_private_mem
>   	if (!kvm || kvm_arch_has_private_mem(kvm))
>   		return KVM_MEMORY_ATTRIBUTE_PRIVATE;
> +#endif
>   
>   	return 0;
>   }
>