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

Fuad Tabba
2024-04-25T14:44:45Z

Hi,

On Fri, Apr 12, 2024 at 9:44 AM Steven Price <steven.price@arm.com> wrote:
>
> Select KVM_GENERIC_PRIVATE_MEM and provide the necessary support
> functions.
>
> Signed-off-by: Steven Price <steven.price@arm.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
>