Re: [PATCH v9 03/41] KVM: Enumerate support for PRIVATE memory iff kvm_arch_has_private_mem is defined

On 7/29/2026 8:35 AM, Ackerley Tng via B4 Relay wrote:
> From: Sean Christopherson <[email protected]>

Though the patch order and diff of this patch is adjusted to what looks 
in v7, per Sean's request [1], the changelog still looks somewhat 
confusing and part incorrect to me.

[1] https://lore.kernel.org/all/[email protected]/

> Explicitly guard reporting support for KVM_MEMORY_ATTRIBUTE_PRIVATE based
> on kvm_arch_has_private_mem being #defined in anticipation of decoupling
> kvm_supported_mem_attributes() from CONFIG_KVM_VM_MEMORY_ATTRIBUTES.

As I commented in v8, the "in anticipation of" thing is not correct.

> guest_memfd support for memory attributes will 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 _somewhere_ would result in KVM over-reporting support on arm64.

1. I'm not sure what "memory attributes being supported somewhere" means.

2. the kvm_supported_mem_attributes() will be renamed to 
kvm_supported_vm_mem_attributes() and it's still under the guard of
CONFIG_KVM_VM_MEMORY_ATTRIBUTES, what's relationship with "guest_memfd 
support for 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]>
> ---
>   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 9f78a466c6f3e..c125d2e8155a7 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 902aa166c9c0c..9501dd8d015d1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2421,8 +2421,10 @@ 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;
>   }
>