Re: [PATCH v6 06/43] arm64: RME: Check for RME support at KVM init

[Gavin Shan]

On 12/13/24 1:55 AM, Steven Price wrote:
> Query the RMI version number and check if it is a compatible version. A
> static key is also provided to signal that a supported RMM is available.
>
> Functions are provided to query if a VM or VCPU is a realm (or rec)
> which currently will always return false.
>
> Signed-off-by: Steven Price <steven.price@xxxxxxx>
> ---
> Changes since v5:
>   * Reword "unsupported" message from "host supports" to "we want" to
>     clarify that 'we' are the 'host'.
> Changes since v2:
>   * Drop return value from kvm_init_rme(), it was always 0.
>   * Rely on the RMM return value to identify whether the RSI ABI is
>     compatible.
> ---
>   arch/arm64/include/asm/kvm_emulate.h | 18 +++++++++
>   arch/arm64/include/asm/kvm_host.h    |  4 ++
>   arch/arm64/include/asm/kvm_rme.h     | 56 ++++++++++++++++++++++++++++
>   arch/arm64/include/asm/virt.h        |  1 +
>   arch/arm64/kvm/Makefile              |  3 +-
>   arch/arm64/kvm/arm.c                 |  6 +++
>   arch/arm64/kvm/rme.c                 | 50 +++++++++++++++++++++++++
>   7 files changed, 137 insertions(+), 1 deletion(-)
>   create mode 100644 arch/arm64/include/asm/kvm_rme.h
>   create mode 100644 arch/arm64/kvm/rme.c

[...]

> +
> +static inline bool kvm_is_realm(struct kvm *kvm)
> +{
> +	if (static_branch_unlikely(&kvm_rme_is_available) && kvm)
> +		return kvm->arch.is_realm;
> +	return false;
> +}
> +

kvm->arch.is_realm won't be true when kvm_rme_is_available is false. It's set
in kvm_arch_init_vm() of PATCH[10]. So it's safe to be simplified as below if
the changes to kvm_arch_init_vm() is slightly modified, more details can be
found from the comments to PATCH[10]

With the changes, we don't have to check kvm_rme_is_available every time.

static inline bool kvm_is_realm(struct kvm *kvm)
{
	return (kvm && kvm->arch.is_realm);
}

Thanks,
Gavin