linux-kernel - Re: [PATCH v6 0/6] iommu/s390: Fixes related to attach and aperture handling

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Date:   Mon, 10 Oct 2022 15:45:49 -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 <robin.murphy@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 0/6] iommu/s390: Fixes related to attach and aperture
 handling

On Mon, Oct 10, 2022 at 04:54:07PM +0200, Niklas Schnelle wrote:
> On Fri, 2022-10-07 at 11:49 +0200, Niklas Schnelle wrote:
> > Hi All,
> > 
> > This is v5 of a follow up to Matt's recent series[0] where he tackled
> > a race that turned out to be outside of the s390 IOMMU driver itself as
> > well as duplicate device attachments. After an internal discussion we came
> > up with what I believe is a cleaner fix. Instead of actively checking for
> > duplicates we instead detach from any previous domain on attach. From my
> > cursory reading of the code this seems to be what the Intel IOMMU driver is
> > doing as well.
> > 
> > Moreover we drop the attempt to re-attach the device to its previous IOMMU
> > domain on failure. This was fragile, unlikely to help and unexpected for
> > calling code. Thanks Jason for the suggestion.
> > 
> > We can also get rid of struct s390_domain_device entirely if we instead
> > thread the list through the attached struct zpci_devs. This saves us from
> > having to allocate during attach and gets rid of one level of indirection
> > during IOMMU operations.
> > 
> > Additionally 3 more fixes have been added in v3 that weren't in v2 of this
> > series. One is for a potential situation where the aperture of a domain
> > could shrink and leave invalid translations. The next one fixes an off by
> > one in checking validity of an IOVA and the last one fixes a wrong value
> > for pgsize_bitmap.
> > 
> > In v4 we also add a patch changing to the map_pages()/unmap_pages()
> > interface in order to prevent a performance regression due to the
> > pgsize_bitmap change.
> > 
> > *Note*:
> > This series is against the s390 features branch[1] which already contains
> > the bus_next field removal that was part of v2.
> > 
> > It is also available as branch iommu_fixes_v6 with the GPG signed tag
> > s390_iommu_fixes_v5 on my niks/linux.git on git.kernel.org[2].
> > 
> > *Open Question*:
> > Which tree should this go via?
> 
> The conflicting commit that removed the bus_next field from struct
> zpci_dev has now made it into Linus' tree via the s390 pull. So this
> series now applies cleanly on mainline master. Still not sure though
> which tree this would best go into.

Arguably it should go through Joerg's iommu tree since it is only in
the iommu driver..

If you need it on a branch to share with the s390 tree then send Joerg
a PR.

Jason