linux-kernel - Re: [PATCH v4 1/5] iommu/s390: Fix duplicate domain attachments

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Date:   Tue, 4 Oct 2022 09:43:38 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>, iommu@...ts.linux.dev,
        linux-s390@...r.kernel.org, borntraeger@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, joro@...tes.org, will@...nel.org,
        robin.murphy@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/5] iommu/s390: Fix duplicate domain attachments

On Tue, Oct 04, 2022 at 02:07:02PM +0200, Niklas Schnelle wrote:
> Since commit fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev
> calls") we can end up with duplicates in the list of devices attached to
> a domain. This is inefficient and confusing since only one domain can
> actually be in control of the IOMMU translations for a device. Fix this
> by detaching the device from the previous domain, if any, on attach.
> Add a WARN_ON() in case we still have attached devices on freeing the
> domain. While here remove the re-attach on failure dance as it was
> determined to be unlikely to help and may confuse debug and recovery.
> 
> Fixes: fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev calls")
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> ---
> v3 -> v4:
> - Drop s390_domain from __s390_iommu_detach_device() (Jason)
> - WARN_ON() mismatched domain in s390_iommu_detach_device() (Jason)
> - Use __s390_iommu_detach_device() in s390_iommu_release_device() (Jason)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason