Re: [PATCH v13 23/48] KVM: arm64: Expose support for private memory

[Wei-Lin Chang]

On Wed, Mar 18, 2026 at 03:53:47PM +0000, Steven Price wrote:
> Select KVM_GENERIC_MEMORY_ATTRIBUTES and provide the necessary support
> functions.
> 
> Signed-off-by: Steven Price <steven.price@xxxxxxx>
> ---
> Changes since v12:
>  * Only define kvm_arch_has_private_mem() when
>    CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES is set to avoid build issues
>    when KVM is disabled.
> Changes since v10:
>  * KVM_GENERIC_PRIVATE_MEM replacd with KVM_GENERIC_MEMORY_ATTRIBUTES.
> Changes since v9:
>  * Drop the #ifdef CONFIG_KVM_PRIVATE_MEM guard from the definition of
>    kvm_arch_has_private_mem()
> Changes since v2:
>  * Switch kvm_arch_has_private_mem() to a macro to avoid overhead of a
>    function call.
>  * Guard definitions of kvm_arch_{pre,post}_set_memory_attributes() with
>    #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES.
>  * Early out in kvm_arch_post_set_memory_attributes() if the WARN_ON
>    should trigger.
> ---
>  arch/arm64/include/asm/kvm_host.h |  4 ++++
>  arch/arm64/kvm/Kconfig            |  1 +
>  arch/arm64/kvm/mmu.c              | 24 ++++++++++++++++++++++++
>  3 files changed, 29 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 64304848aad4..1efea996f474 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1486,6 +1486,10 @@ struct kvm *kvm_arch_alloc_vm(void);
>  
>  #define vcpu_is_protected(vcpu)		kvm_vm_is_protected((vcpu)->kvm)
>  
> +#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
> +#define kvm_arch_has_private_mem(kvm) ((kvm)->arch.is_realm)
> +#endif
> +
>  int kvm_arm_vcpu_finalize(struct kvm_vcpu *vcpu, int feature);
>  bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
>  
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index 4f803fd1c99a..1cac6dfc0972 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -38,6 +38,7 @@ menuconfig KVM
>  	select SCHED_INFO
>  	select GUEST_PERF_EVENTS if PERF_EVENTS
>  	select KVM_GUEST_MEMFD
> +	select KVM_GENERIC_MEMORY_ATTRIBUTES

Hi,

I believe we should also add this:

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index bfa0ab343081..13722f876dcd 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6365,7 +6365,7 @@ Returns -EINVAL if called on a protected VM.
 -------------------------------
 
 :Capability: KVM_CAP_MEMORY_ATTRIBUTES
-:Architectures: x86
+:Architectures: x86, arm64
 :Type: vm ioctl
 :Parameters: struct kvm_memory_attributes (in)
 :Returns: 0 on success, <0 on error

Thanks,
Wei-Lin Chang

>  	help
>  	  Support hosting virtualized guest machines.
>  
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index b705ad6c6c8b..bad93938acdb 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -2494,6 +2494,30 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  	return ret;
>  }
>  
> +#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
> +bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm,
> +					struct kvm_gfn_range *range)
> +{
> +	WARN_ON_ONCE(!kvm_arch_has_private_mem(kvm));
> +	return false;
> +}
> +
> +bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
> +					 struct kvm_gfn_range *range)
> +{
> +	if (WARN_ON_ONCE(!kvm_arch_has_private_mem(kvm)))
> +		return false;
> +
> +	if (range->arg.attributes & KVM_MEMORY_ATTRIBUTE_PRIVATE)
> +		range->attr_filter = KVM_FILTER_SHARED;
> +	else
> +		range->attr_filter = KVM_FILTER_PRIVATE;
> +	kvm_unmap_gfn_range(kvm, range);
> +
> +	return false;
> +}
> +#endif
> +
>  void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
>  {
>  }
> -- 
> 2.43.0
>