linux-kernel - Re: [PATCH v2 42/43] arm64: kvm: Expose support for private memory

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Message-ID: <CA+EHjTyGcO=-EdFE75g5DwBKosKWUdmg7CB8VAr1w78C=2PCww@mail.gmail.com>
Date: Thu, 25 Apr 2024 15:44:07 +0100
From: Fuad Tabba <tabba@...gle.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, 
	Joey Gouly <joey.gouly@....com>, Alexandru Elisei <alexandru.elisei@....com>, 
	Christoffer Dall <christoffer.dall@....com>, linux-coco@...ts.linux.dev, 
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
Subject: Re: [PATCH v2 42/43] arm64: kvm: Expose support for private memory

Hi,

On Fri, Apr 12, 2024 at 9:44 AM Steven Price <steven.price@....com> wrote:
>
> Select KVM_GENERIC_PRIVATE_MEM and provide the necessary support
> functions.
>
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>  arch/arm64/include/asm/kvm_host.h |  4 ++++
>  arch/arm64/kvm/Kconfig            |  1 +
>  arch/arm64/kvm/arm.c              |  5 +++++
>  arch/arm64/kvm/mmu.c              | 19 +++++++++++++++++++
>  4 files changed, 29 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 902923402f6e..93de7f5009fe 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1259,6 +1259,10 @@ static inline bool kvm_vm_is_protected(struct kvm *kvm)
>         return false;
>  }
>
> +#ifdef CONFIG_KVM_PRIVATE_MEM
> +bool kvm_arch_has_private_mem(struct kvm *kvm);
> +#endif
> +

I think it might be better to define kvm_arch_has_private_mem() for
both cases, whether KVM_PRIVATE_MEM is enabled or not, similar to the
way it's defined in arch/x86/include/asm/kvm_host.h

>  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 58f09370d17e..8da57e74c86a 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

I don't think this should be enabled by default, but should depend on
whether RME is configured. That said, I can't find the config option
for RME...

>         help
>           Support hosting virtualized guest machines.
>
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 2dd014d3c366..a66d0a6eb4fa 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -89,6 +89,11 @@ int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
>         return kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE;
>  }
>
> +bool kvm_arch_has_private_mem(struct kvm *kvm)
> +{
> +       return kvm_is_realm(kvm);
> +}
> +

Related to my earlier comment on kvm_arch_has_private_mem(), and
considering how often this function is called, wouldn't it be better
to define this in a way similar to arch/x86/include/asm/kvm_host.h ?


>  int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>                             struct kvm_enable_cap *cap)
>  {
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 48c957e21c83..808bceebad4d 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -2171,6 +2171,25 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>         return ret;
>  }

The following two functions should be gated by

#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)
> +{
> +       WARN_ON_ONCE(!kvm_arch_has_private_mem(kvm));

I think this should return here, not just warn.

Cheers,
/fuad

> +
> +       if (range->arg.attributes & KVM_MEMORY_ATTRIBUTE_PRIVATE)
> +               range->only_shared = true;
> +       kvm_unmap_gfn_range(kvm, range);
> +
> +       return false;
> +}
> +
>  void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
>  {
>  }
> --
> 2.34.1
>