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

Steven Price
2026-03-20T16:39:23Z

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@arm.com>
>> ---
>> 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
>>