Re: [PATCH v5 5/5] pci: Suspend iommu function prior to resetting a device

[Nicolin Chen <nicolinc@nvidia.com>]

On Fri, Nov 14, 2025 at 09:45:31AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > Sent: Tuesday, November 11, 2025 1:13 PM
> > 
> > PCIe permits a device to ignore ATS invalidation TLPs, while processing a
> > reset. This creates a problem visible to the OS where an ATS invalidation
> > command will time out: e.g. an SVA domain will have no coordination with a
> > reset event and can racily issue ATS invalidations to a resetting device.
> > 
> > The PCIe spec in sec 10.3.1 IMPLEMENTATION NOTE recommends to disable
> > and
> > block ATS before initiating a Function Level Reset. It also mentions that
> > other reset methods could have the same vulnerability as well.
> > 
> > Now iommu_dev_reset_prepare/done() helpers are introduced for this
> > matter.
> > Use them in all the existing reset functions, which will attach the device
> 
> looks pci_reset_bus_function() was missed?

Will add that.

> > @@ -971,6 +971,7 @@ void pci_set_acpi_fwnode(struct pci_dev *dev)
> >  int pci_dev_acpi_reset(struct pci_dev *dev, bool probe)
> >  {
> >  	acpi_handle handle = ACPI_HANDLE(&dev->dev);
> > +	int ret = 0;
> 
> no need to initialize it. ditto for other reset functions.

Ack.

> > +/*
> > + * Per PCIe r6.3, sec 10.3.1 IMPLEMENTATION NOTE, software disables ATS
> > before
> > + * initiating a reset. Notify the iommu driver that enabled ATS.
> > + */
> > +int pci_reset_iommu_prepare(struct pci_dev *dev)
> > +{
> > +	if (pci_ats_supported(dev))
> > +		return iommu_dev_reset_prepare(&dev->dev);
> > +	return 0;
> > +}
> 
> the comment says "driver that enabled ATS", but the code checks
> whether ATS is supported.
> 
> which one is desired?

The comments says "the iommu driver that enabled ATS". It doesn't
conflict with what the PCI core checks here?

> > +	/* Have to call it after waiting for pending DMA transaction */
> > +	ret = pci_reset_iommu_prepare(dev);
> > +	if (ret) {
> > +		pci_err(dev, "failed to stop IOMMU\n");
> 
> the error message could be more informative.

OK. Perhaps print the ret value.

Thanks!
Nicolin