linux-kernel - Re: [PATCH RFCv2 07/13] iommufd: Implement sw

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Message-ID: <20250123193006.GA1056867@nvidia.com>
Date: Thu, 23 Jan 2025 15:30:06 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: will@...nel.org, robin.murphy@....com, kevin.tian@...el.com,
	tglx@...utronix.de, maz@...nel.org, alex.williamson@...hat.com,
	joro@...tes.org, shuah@...nel.org, reinette.chatre@...el.com,
	eric.auger@...hat.com, yebin10@...wei.com, apatel@...tanamicro.com,
	shivamurthy.shastri@...utronix.de, bhelgaas@...gle.com,
	anna-maria@...utronix.de, yury.norov@...il.com, nipun.gupta@....com,
	iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
	linux-kselftest@...r.kernel.org, patches@...ts.linux.dev,
	jean-philippe@...aro.org, mdf@...nel.org, mshavit@...gle.com,
	shameerali.kolothum.thodi@...wei.com, smostafa@...gle.com,
	ddutile@...hat.com
Subject: Re: [PATCH RFCv2 07/13] iommufd: Implement sw_msi support natively

On Fri, Jan 10, 2025 at 07:32:23PM -0800, Nicolin Chen wrote:

> +/*
> + * FIXME: when a domain is removed any ids that are not in the union of
> + * all still attached devices should be removed.
> + */

I've been thinking about this, maybe we can just delete the comment.

It is thinking about is the case where you attach a domain to device
A, then B, then detach B. If there are multiple ITS pages then B's
page will remain accessible to A.

However, A had access to B's page already and it was perfectly fine,
so why do we need to revoke it?

The logic is fine to keep track of this, so I think we can just let it
be. ITS pages populate in a lazy way, but are permanent once
populated.

Jason