linux-kernel - Re: [PATCH] [RFC] KVM: arm64/vgic: Populate GICR

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Message-ID: <ZcIJzn9KLR_bWdwc@linux.dev>
Date: Tue, 6 Feb 2024 10:28:30 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: Saurav Sachidanand <sauravsc@...zon.com>
Cc: Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFC] KVM: arm64/vgic: Populate GICR_TYPER with Aff3

Hi Saurav,

On Mon, Feb 05, 2024 at 06:43:26PM +0000, Saurav Sachidanand wrote:

[...]

> diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> index c15ee1df036a..26bc838ce14c 100644
> --- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> +++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
> @@ -324,6 +324,7 @@ static unsigned long vgic_mmio_read_v3r_typer(struct kvm_vcpu *vcpu,
>  	u64 value;
>  
>  	value = (u64)(mpidr & GENMASK(23, 0)) << 32;
> +	value |= (u64)((mpidr >> 32) & GENMASK(7, 0)) << 56;

This looks suspiciously similar to what MPIDR_AFFINITY_LEVEL()
accomplishes. I think we can tolerate a few extra lines of code to make
the entire thing more self-documenting, like:

	value = ((u64)MPIDR_AFFINITY_LEVEL(mpidr, 3) << 56 |
		MPIDR_AFFINITY_LEVEL(mpidr, 2) << 48 |
		MPIDR_AFFINITY_LEVEL(mpidr, 1) << 40 |
		MPIDR_AFFINITY_LEVEL(mpidr, 0) << 32);

-- 
Thanks,
Oliver