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

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Message-ID: <7271b3ff-8665-4a98-b3dd-77417f85d5e3@redhat.com>
Date: Wed, 29 Jan 2025 13:57:23 +1000
From: Gavin Shan <gshan@...hat.com>
To: Steven Price <steven.price@....com>, kvm@...r.kernel.org,
 kvmarm@...ts.linux.dev
Cc: 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>, Fuad Tabba <tabba@...gle.com>,
 linux-coco@...ts.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
 Shanker Donthineni <sdonthineni@...dia.com>, Alper Gun
 <alpergun@...gle.com>, "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>
Subject: Re: [PATCH v6 06/43] arm64: RME: Check for RME support at KVM init

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