linux-kernel - Re: [RFC PATCH v2 00/58] KVM: Arm SMMUv3 driver for pKVM

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Message-ID: <20250116191952.GD674319@ziepe.ca>
Date: Thu, 16 Jan 2025 15:19:52 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Mostafa Saleh <smostafa@...gle.com>
Cc: iommu@...ts.linux.dev, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	catalin.marinas@....com, will@...nel.org, maz@...nel.org,
	oliver.upton@...ux.dev, joey.gouly@....com, suzuki.poulose@....com,
	yuzenghui@...wei.com, robdclark@...il.com, joro@...tes.org,
	robin.murphy@....com, jean-philippe@...aro.org, nicolinc@...dia.com,
	vdonnefort@...gle.com, qperret@...gle.com, tabba@...gle.com,
	danielmentz@...gle.com, tzukui@...gle.com
Subject: Re: [RFC PATCH v2 00/58] KVM: Arm SMMUv3 driver for pKVM

On Wed, Jan 08, 2025 at 12:09:53PM +0000, Mostafa Saleh wrote:

> I am open to gradually upstream this as you mentioned where as a first
> step pKVM would establish DMA isolation without translation for host,
> that should be enough to have functional pKVM and run protected workloads.

Personally I hate these giant patch series, you should strip it down
to small meaningful steps and try to stay below 20 per series.

I think getting pkvm to own the SMMU HW is a great first step that
everything else can build on

> But although that might be usable on some systems, I don’t think that’s
> practical in the long term as it limits the amount of HW that can run pKVM.

I suspect you will end up doing everything. Old HW needs paravirt, new
HW will want nesting and its performance. Users other than mobile will
come. If we were to use pKVM on server workloads we need nesting for
performance.

Jason