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

[Steven Price]

On 19/03/2026 19:01, Wei-Lin Chang wrote:
> 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

Good spot.

Thanks,
Steve

> 
> 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
>>