linux-kernel - Re: [RFC 11/18] dma-iommu: Always enable deferred attaches for liveupdate

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Message-ID: <20240205174507.GD31743@ziepe.ca>
Date: Mon, 5 Feb 2024 13:45:07 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: James Gowans <jgowans@...zon.com>
Cc: linux-kernel@...r.kernel.org, Eric Biederman <ebiederm@...ssion.com>,
	kexec@...ts.infradead.org, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, iommu@...ts.linux.dev,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	linux-fsdevel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
	Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Alexander Graf <graf@...zon.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	"Jan H . Schoenherr" <jschoenh@...zon.de>,
	Usama Arif <usama.arif@...edance.com>,
	Anthony Yznaga <anthony.yznaga@...cle.com>,
	Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
	madvenka@...ux.microsoft.com, steven.sistare@...cle.com,
	yuleixzhang@...cent.com
Subject: Re: [RFC 11/18] dma-iommu: Always enable deferred attaches for
 liveupdate

On Mon, Feb 05, 2024 at 12:01:56PM +0000, James Gowans wrote:
> Seeing as translations are pre-enabled, all devices will be set for
> deferred attach. The deferred attached actually has to be done when
> doing DMA mapping for devices to work.

This shouldn't be part of your solution..

A DMA API using driver should never be attached to a device that is
being persisted across a kexec. If it does then the device should be
fully reset and re-attached to the normal DMA API iommu domain.

You should be striving to have an iommu_domain to represent the
special post-kexec translation regime.

Jason