On 2022-05-04 15:54, Jason Gunthorpe wrote:
On Wed, May 04, 2022 at 03:42:09PM +0100, Robin Murphy wrote:
This fixes an oops with VFIO and SMMUv3 because VFIO will call
iommu_detach_group() and then immediately iommu_domain_free(), but
SMMUv3 has no way to know that the domain it is holding a pointer to
has been freed. Now the iommu_detach_group() will assign the blocking
domain and SMMUv3 will no longer hold a stale domain reference.
Thanks for taking this on! I do like the overall structure and naming much
more than my initial sketch :)
Thanks, no problem!
/*
- * If the group has been claimed already, do not re-attach the default
- * domain.
+ * A NULL domain means to call the detach_dev() op. New drivers should
+ * use a IOMMU_DOMAIN_IDENTITY domain instead of a NULL default_domain
Nit: IOMMU_DOMAIN_DMA is the baseline of default domain support, passthrough
is more of an optional extra.
Can you elaborate on this a bit more for the comment, I'm not sure I
understand all the historical stuff here.
Well, the comment could effectively just be "New drivers should support
default domains."
What supporting default domains means in practice is two things: that
.attach_dev handles moving directly between domains without .detach_dev
being called, and that .domain_alloc supports at least IOMMU_DOMAIN_DMA
- other unsupported default domain types can fall back to that, but not
vice versa, see iommu_group_alloc_default_domain().
Here we are looking at a case where group->domain becomes NULL - what
does this mean in the historical world? ie what should the iommu
driver do when detach_dev is called?
I had guessed it was remove all translation - ie IOMMU_DOMAIN_IDENTITY?
Historically, whatever a NULL domain means is mostly between the IOMMU
driver and the platform DMA ops - I honestly have no idea what the likes
of s390 and fsl-pamu do, for example. For SMMUv3 it was always configurable.
Cheers,
Robin.
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