linux-kernel - Re: [PATCH v11 2/6] KVM: arm64: Use SMCCC 1.2 for FF-A initialization and in host handler

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Message-ID: <aL7qghmPfM3NMyMz@willie-the-truck>
Date: Mon, 8 Sep 2025 15:38:58 +0100
From: Will Deacon <will@...nel.org>
To: perlarsen@...gle.com
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Sudeep Holla <sudeep.holla@....com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, ahomescu@...gle.com,
	armellel@...gle.com, arve@...roid.com, ayrton@...gle.com,
	qperret@...gle.com, sebastianene@...gle.com, qwandor@...gle.com
Subject: Re: [PATCH v11 2/6] KVM: arm64: Use SMCCC 1.2 for FF-A
 initialization and in host handler

On Wed, Aug 20, 2025 at 01:10:06AM +0000, Per Larsen via B4 Relay wrote:
> From: Per Larsen <perlarsen@...gle.com>
> 
> SMCCC 1.1 and prior allows four registers to be sent back as a result
> of an FF-A interface. SMCCC 1.2 increases the number of results that can
> be sent back to 8 and 16 for 32-bit and 64-bit SMC/HVCs respectively.
> 
> FF-A 1.0 references SMCCC 1.2 (reference [4] on page xi) and FF-A 1.2
> explicitly requires SMCCC 1.2 so it should be safe to use this version
> unconditionally. Moreover, it is simpler to implement FF-A features
> without having to worry about compatibility with SMCCC 1.1 and older.
> 
> SMCCC 1.2 requires that SMC32/HVC32 from aarch64 mode preserves x8-x30
> but given that there is no reliable way to distinguish 32-bit/64-bit
> calls, we assume SMC64 unconditionally. This has the benefit of being
> consistent with the handling of calls that are passed through, i.e., not
> proxied. (A cleaner solution will become available in FF-A 1.3.)
> 
> Update the FF-A initialization and host handler code to use SMCCC 1.2.
> 
> Signed-off-by: Per Larsen <perlarsen@...gle.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/Makefile |   1 +
>  arch/arm64/kvm/hyp/nvhe/ffa.c    | 193 +++++++++++++++++++++++++--------------
>  2 files changed, 125 insertions(+), 69 deletions(-)

Acked-by: Will Deacon <will@...nel.org>

Will