Messages in this thread | | | Date | Mon, 29 Aug 2022 11:49:23 +0800 | Subject | Re: [PATCH v2 1/3] iommu: Replace detach_dev with real blocking domains | From | Baolu Lu <> |
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On 2022/8/26 23:34, Jason Gunthorpe wrote: > On Fri, Aug 26, 2022 at 08:30:12PM +0800, Lu Baolu wrote: >> From iommu core's point of view, detaching a domain from a device is >> equal to attaching the group's blocking domain to the device. This >> repalces all detach_dev callbacks in the IOMMU drivers with a real >> blocking domain and handles detaching domain through it. > > There is a subtly here, where detach_dev() is not *always* going to a > blocking domain. Recall we made this mistaken when building the owner > series and it is why the blocking domain was introduced. > > The challenge with this work is to be sure that the code you assigned > to the blocking domain doesn't actually set an identity domain or > set things to use the platform DMA ops.
This looks like a defect in the current IOMMU subsystem.
> >> +static int blocking_domain_attach_dev(struct iommu_domain *_domain, >> + struct device *dev) >> +{ >> + struct iommu_domain *domain = iommu_get_domain_for_dev(dev); >> + >> + s390_iommu_detach_device(domain, dev); >> + >> + return 0; >> +} > > For instance, I know that this is returning the group back to the > platform DMA ops. > > To really make progress on this I would suggest > > 1) Remove detach_dev from drivers that don't use it. This is any > driver that provides a default domain, if a default domain is set > then we always use attach_dev(default_domain) and never detach_dev > > 2) Of those drivers in #1 audit and try to determine if their > detach_dev is doing blocking domain behavior and if yes give them a > real blocking domain. Otherwise just delete the code. > > 3) The remaining drivers are not using default_domain. Rename > 'detach_dev' to iommu_ops->set_platform_dma(dev) to make it clear > that what it is doing is returning control back to the platform DMA > ops. > > I would do one patch per driver on the blocking domain conversions and > get acks from the driver owners. Do as many as can be acked, delete > the rest. > > Make it clear to driver owners checking that blocking domain must halt > all DMA, and it must not be a passthrough or identity behavior. > > When last I looked several of the drivers looked like they were > setting an identity domain on the detach_dev - eg back to a boot time > behavior where the iommu is bypassed. It is really important these not > be converted to blocking :) Arguably if they can be found they should > be converted to identity domains instead.
Above makes sense to me. Thanks! I will spend some time looking into each IOMMU driver and back here after I work through all of them.
Best regards, baolu
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