linux-kernel - Re: [RFC PATCH v1 03/37] KVM: Enumerate support for PRIVATE memory iff kvm_arch_has_private

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Message-ID: <f2bfa5ad-4c74-4b6d-baa7-d0d01d5d9b15@linux.intel.com>
Date: Thu, 13 Nov 2025 09:42:22 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Ackerley Tng <ackerleytng@...gle.com>
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Subject: Re: [RFC PATCH v1 03/37] KVM: Enumerate support for PRIVATE memory
 iff kvm_arch_has_private_mem is defined



On 10/18/2025 4:11 AM, Ackerley Tng wrote:
> From: Sean Christopherson <seanjc@...gle.com>
>
> 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.
> guest_memfd support for memory attributes will be unconditional to avoid
> yet more macros (all architectures that support guest_memfd are expect to
  expect -> expected

> user per-gmem attributes at some point), at which point enumerating support
    ^
   use
> KVM_MEMORY_ATTRIBUTE_PRIVATE based solely on memory attributes being
> supported _somewhere_ would result in KVM over-reporting support on arm64.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   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 fddb373fcbaaf..21bf30e8d3cc1 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -721,7 +721,7 @@ 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 f73047ea4333e..591795a3fa124 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2428,8 +2428,10 @@ 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;
>   }