Re: [RFC PATCH 1/5] PCI: Refuse function reset of an SR-IOV PF with enabled VFs

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Aug 20, 2026 at 10:38:07PM +0000, Samiullah Khawaja wrote:

> > The blocking domain operation looks like it might be simplest to
> > implement in the IOMMU core.  We can set a flag for a default blocking
> > domain on the IOMMU group when we take_dma_ownership of the group.  Then
> > release_dma_ownership picks the blocking rather than default domain.
> > 
> > This is then unwound in use_default_domain, called via dma_configure,
> > attaching the device to the default domain in probe of the next driver.
> > Therefore until probe by another driver, a device used by vfio would
> > remain in a blocking domain even while unused and unbound.
> 
> The devices are expected to be attached to the default_domain even when
> these are unbound and the use_default_domain assumes that, and it only
> checks the ownership and doesn't switch the domain to default_domain. I
> guess we should add a WARN in use_default_domain() if that is not true.
> I will probably send out a patch for that separately.
> 
> I think we can move the device back to default_domain after reset after
> unbind, maybe it can be done in pci_dma_cleanup() based on
> driver_managed_dma?

This blocking domain stuff sounds very similar to what Nicolin
implemented for the per-function ATS issue?

Broadly we must setup a blocking domain in the iommu if ATS is
available across reset or you get these ATS related issues.

I think at the time he looked at doing SRIOV as well but it was
tricky..

Jason