RE: [PATCH] iommu/vt-d: Handle hotplug devices' default identity mapping setting

From: James Dong
Date: Fri Feb 22 2019 - 02:37:15 EST


Sorry that my last reply email seems not text format. Resend it now.

Thanks for your comments and your patch. Please find below our responses to
each of your comments:

> What does "I/O operation won't work" exactly mean here? Do you see any
> IOMMU fault message? Or, something doesn't work as expected?

Yes, DMAR fault messages as following came out:
[ 354.939896] DMAR: DMAR:[DMA Read] Request device [03:00.1]fault addr 1fdfe80000
[ 354.939896] DMAR:[fault reason 02] Present bit in context entry is clear

> Do you mind checking this?
> index 6ecdcf8fc8c0..f62f30bc1339 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -2632,6 +2632,9 @@ static struct dmar_domain
> *find_or_alloc_domain(struct device *dev, int gaw)
> goto out;
> }
> + if (!iommu_should_identity_map(dev, 0))
> + return si_domain;
> +
> /* Allocate and initialize new domain for the device */
> domain = alloc_domain(0);
> if (!domain)

Tried this patch, and the same DMAR fault message came out.

Guess it is because of the iommu code path for hotplug devices. If a hotplug
device is rescanned after removal, iommu_bus_notifier will be called as part
of the notifier chains to handle BUS_NOTIFY_ADD_DEVICE event. Along the code
path, intel_iommu_ops->add_device() created an iommu group for this hotplug
device, but failed to create an iommu domain because of the default domain
type IOMMU_DOMAIN_IDENTITY imposed by current IOMMU command line option got
declined by intel_iommu_ops->domain_alloc().

Since si_domain is type of "struct dmar_domain", which is platform dependent,
it is hard to make this change in intel_iommu_ops->domain_alloc().

In your patch, function find_or_alloc_domain() is not in the code path of
BUS_NOTIFY_ADD_DEVICE event notifier chain.

Please let us know if your have more concerns and suggestions.

Best Regards,