linux-kernel - Re: [PATCH v7 13/14] iommu/arm-smmu-v3: Report events that belong to devices attached to vIOMMU

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Message-ID: <Z7304KKv2c1pOhj2@google.com>
Date: Tue, 25 Feb 2025 16:50:40 +0000
From: Pranjal Shrivastava <praan@...gle.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, kevin.tian@...el.com,
	corbet@....net, will@...nel.org, joro@...tes.org,
	suravee.suthikulpanit@....com, robin.murphy@....com,
	dwmw2@...radead.org, baolu.lu@...ux.intel.com, shuah@...nel.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
	eric.auger@...hat.com, jean-philippe@...aro.org, mdf@...nel.org,
	mshavit@...gle.com, shameerali.kolothum.thodi@...wei.com,
	smostafa@...gle.com, ddutile@...hat.com, yi.l.liu@...el.com,
	patches@...ts.linux.dev
Subject: Re: [PATCH v7 13/14] iommu/arm-smmu-v3: Report events that belong to
 devices attached to vIOMMU

On Mon, Feb 24, 2025 at 07:35:05PM -0400, Jason Gunthorpe wrote:
> On Mon, Feb 24, 2025 at 01:56:46PM -0800, Nicolin Chen wrote:
> 
> > > Just thinking out loud here:
> > > I understand the goal here is to "emulate" an IOMMU. But I'm just
> > > wondering if we could report struct events instead of the raw event?
> > > 
> > > For example, can't we have something like arm_smmu_event here with the
> > > sid changed to vsid? 
> > > 
> > > Are we taking the raw event since we want to keep the `u64 event_data[]`
> > > field within `struct iommufd_vevent` generic to all architectures?
> > 
> > The ABIs for vSMMU are defined in the HW languange, e.g. cmd, ste.
> > Thus, here evt in raw too.
> 
> Right, the point is that it gives as a safe uABI that is effectively
> being managed by ARM.
> 
> If we make our own thing then we have to take the responsiblity to
> make it safe and extensible. I don't see a justification to do that..
> 
> It is the same discussion we had around the vSTE as input, the raw
> invalidation command and the IDRs. Since we've already done 'follow
> the SMMU spec' so many times already now we should keep doing it.

Ack. Undertsood. Thanks for the explanation :)

-Praan