linux-kernel - Re: [PATCH v9 41/43] KVM: arm64: Expose support for private memory

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Message-ID: <20250612151427.GA1913753@e124191.cambridge.arm.com>
Date: Thu, 12 Jun 2025 16:14:27 +0100
From: Joey Gouly <joey.gouly@....com>
To: Steven Price <steven.price@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	James Morse <james.morse@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Alexandru Elisei <alexandru.elisei@....com>,
	Christoffer Dall <christoffer.dall@....com>,
	Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
	Gavin Shan <gshan@...hat.com>,
	Shanker Donthineni <sdonthineni@...dia.com>,
	Alper Gun <alpergun@...gle.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@...nel.org>,
	Emi Kisanuki <fj0570is@...itsu.com>
Subject: Re: [PATCH v9 41/43] KVM: arm64: Expose support for private memory

Hi Steven,

On Wed, Jun 11, 2025 at 11:48:38AM +0100, Steven Price wrote:
> Select KVM_GENERIC_PRIVATE_MEM and provide the necessary support
> functions.
> 
> Signed-off-by: Steven Price <steven.price@....com>
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> ---
> 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 |  6 ++++++
>  arch/arm64/kvm/Kconfig            |  1 +
>  arch/arm64/kvm/mmu.c              | 24 ++++++++++++++++++++++++
>  3 files changed, 31 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index a1857802db64..9903b0e8ef3f 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1514,6 +1514,12 @@ struct kvm *kvm_arch_alloc_vm(void);
>  
>  #define vcpu_is_protected(vcpu)		kvm_vm_is_protected((vcpu)->kvm)
>  
> +#ifdef CONFIG_KVM_PRIVATE_MEM
> +#define kvm_arch_has_private_mem(kvm) ((kvm)->arch.is_realm)
> +#else
> +#define kvm_arch_has_private_mem(kvm) false
> +#endif

I don't understand the ifdef here (or below). In the Kconfig you 'select
KVM_GENERIC_PRIVATE_MEM', so it will always be on/defined? Unless I'm
misunderstanding something.

> +
>  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 713248f240e0..3a04b040869d 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -37,6 +37,7 @@ menuconfig KVM
>  	select HAVE_KVM_VCPU_RUN_PID_CHANGE
>  	select SCHED_INFO
>  	select GUEST_PERF_EVENTS if PERF_EVENTS
> +	select KVM_GENERIC_PRIVATE_MEM
>  	help
>  	  Support hosting virtualized guest machines.
>  
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 580ed362833c..c866891fd8f9 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -2384,6 +2384,30 @@ 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
> 

Thanks,
Joey