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

From: Niklas Schnelle
Date: Mon Oct 10 2022 - 10:54:31 EST

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[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.

> Best regards,
> Niklas