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

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Message-ID: <Z5DahnNdoShXesib@google.com>
Date: Wed, 22 Jan 2025 11:46:14 +0000
From: Mostafa Saleh <smostafa@...gle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
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 Thu, Jan 16, 2025 at 03:19:52PM -0400, Jason Gunthorpe wrote:
> 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

I plan to do that for v3, I think that also removes the out-of-tree
dependencies, so the code applies directly on upstream.
Thanks for the feedback!

> 
> > 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.

Yes, I guess that would be the case, as I mentioned in another reply
it would be interesting to get the order of magnitude both, which I am
looking into, I hope it'd help with which direction we should
prioritize upstream.

Thanks,
Mostafa

> 
> Jason