Re: [PATCH v9 2/5] iommu: Implement of_iommu_get_resv_regions()

[Thierry Reding <thierry.reding@gmail.com>]

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On Fri, Oct 07, 2022 at 02:47:23PM +0100, Robin Murphy wrote:
> On 2022-09-23 13:35, Thierry Reding wrote:
> > From: Thierry Reding <treding@nvidia.com>
> > 
> > This is an implementation that IOMMU drivers can use to obtain reserved
> > memory regions from a device tree node. It uses the reserved-memory DT
> > bindings to find the regions associated with a given device. If these
> > regions are marked accordingly, identity mappings will be created for
> > them in the IOMMU domain that the devices will be attached to.
> > 
> > Cc: Frank Rowand <frowand.list@gmail.com>
> > Cc: devicetree@vger.kernel.org
> > Reviewed-by: Rob Herring <robh@kernel.org>
> > Signed-off-by: Thierry Reding <treding@nvidia.com>
> > ---
> > Changes in v9:
> > - address review comments by Robin Murphy:
> >    - warn about non-direct mappings since they are not supported yet
> >    - cleanup code to require less indentation
> >    - narrow scope of variables
> > 
> > Changes in v8:
> > - cleanup set-but-unused variables
> > 
> > Changes in v6:
> > - remove reference to now unused dt-bindings/reserved-memory.h include
> > 
> > Changes in v5:
> > - update for new "iommu-addresses" device tree bindings
> > 
> > Changes in v4:
> > - fix build failure on !CONFIG_OF_ADDRESS
> > 
> > Changes in v3:
> > - change "active" property to identity mapping flag that is part of the
> >    memory region specifier (as defined by #memory-region-cells) to allow
> >    per-reference flags to be used
> > 
> > Changes in v2:
> > - use "active" property to determine whether direct mappings are needed
> > 
> >   drivers/iommu/of_iommu.c | 104 +++++++++++++++++++++++++++++++++++++++
> >   include/linux/of_iommu.h |   8 +++
> >   2 files changed, 112 insertions(+)
> > 
> > diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> > index 5696314ae69e..0bf2b08bca0a 100644
> > --- a/drivers/iommu/of_iommu.c
> > +++ b/drivers/iommu/of_iommu.c
> > @@ -11,6 +11,7 @@
> >   #include <linux/module.h>
> >   #include <linux/msi.h>
> >   #include <linux/of.h>
> > +#include <linux/of_address.h>
> >   #include <linux/of_iommu.h>
> >   #include <linux/of_pci.h>
> >   #include <linux/pci.h>
> > @@ -172,3 +173,106 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
> >   	return ops;
> >   }
> > +
> > +static inline bool check_direct_mapping(struct device *dev, struct resource *phys,
> 
> Where "phys" is the virtual address, right? :(

No, phys is actually res passed in from of_iommu_get_resv_regions()
where it is the address read from the "reg" property. So that's the
physical address of the reserved region. Perhaps it'd be useful to
rename "res" to "phys" in that function to be a little more consistent.
It's actually the "start" and "end" values that are passed into this
function that refer to the I/O virtual addresses from iommu-addresses.

> 
> > +					phys_addr_t start, phys_addr_t end)
> > +{
> > +	if (start != phys->start || end != phys->end) {
> > +		dev_warn(dev, "treating non-direct mapping [%pr] -> [%pap-%pap] as reservation\n",
> > +			 &phys, &start, &end);
> > +		return false;
> > +	}
> > +
> > +	return true;
> > +}
> > +
> > +/**
> > + * of_iommu_get_resv_regions - reserved region driver helper for device tree
> > + * @dev: device for which to get reserved regions
> > + * @list: reserved region list
> > + *
> > + * IOMMU drivers can use this to implement their .get_resv_regions() callback
> > + * for memory regions attached to a device tree node. See the reserved-memory
> > + * device tree bindings on how to use these:
> > + *
> > + *   Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> > + */
> > +void of_iommu_get_resv_regions(struct device *dev, struct list_head *list)
> > +{
> > +#if IS_ENABLED(CONFIG_OF_ADDRESS)
> > +	struct of_phandle_iterator it;
> > +	int err;
> > +
> > +	of_for_each_phandle(&it, err, dev->of_node, "memory-region", NULL, 0) {
> > +		const __be32 *maps, *end;
> > +		struct resource res;
> > +		int size;
> > +
> > +		memset(&res, 0, sizeof(res));
> > +
> > +		/*
> > +		 * The "reg" property is optional and can be omitted by reserved-memory regions
> > +		 * that represent reservations in the IOVA space, which are regions that should
> > +		 * not be mapped.
> > +		 */
> > +		if (of_find_property(it.node, "reg", NULL)) {
> > +			err = of_address_to_resource(it.node, 0, &res);
> > +			if (err < 0) {
> > +				dev_err(dev, "failed to parse memory region %pOF: %d\n",
> > +					it.node, err);
> > +				continue;
> > +			}
> > +		}
> > +
> > +		maps = of_get_property(it.node, "iommu-addresses", &size);
> > +		if (!maps)
> > +			continue;
> > +
> > +		end = maps + size / sizeof(__be32);
> > +
> > +		while (maps < end) {
> > +			struct device_node *np;
> > +			u32 phandle;
> > +			int na, ns;
> > +
> > +			phandle = be32_to_cpup(maps++);
> > +			np = of_find_node_by_phandle(phandle);
> > +			na = of_n_addr_cells(np);
> > +			ns = of_n_size_cells(np);
> > +
> > +			if (np == dev->of_node) {
> > +				int prot = IOMMU_READ | IOMMU_WRITE;
> > +				struct iommu_resv_region *region;
> > +				enum iommu_resv_type type;
> > +				phys_addr_t start;
> > +				size_t length;
> > +
> > +				start = of_translate_dma_address(np, maps);
> > +				length = of_read_number(maps + na, ns);
> > +
> > +				/*
> > +				 * IOMMU regions without an associated physical region cannot be
> > +				 * mapped and are simply reservations.
> > +				 */
> > +				if (res.end > res.start) {
> > +					phys_addr_t end = start + length - 1;
> > +
> > +					if (check_direct_mapping(dev, &res, start, end))
> > +						type = IOMMU_RESV_DIRECT_RELAXABLE;
> 
> Again I really don't think we should assume relaxable by default.
> 
> Looking at the shape of things now, it seems like check_direct_mappings()
> wants to subsume the check on res as well and grow in to a more general
> function for determining the iommu_resv_type. Then we've got a clear place
> to start special-casing things like simple-framebuffer that we do know a bit
> more about.

Okay, I think I know where you're going with this. Let me see what I can
come up with.

Thierry

> 
> Thanks,
> Robin.
> 
> > +					else
> > +						type = IOMMU_RESV_RESERVED;
> > +				} else {
> > +					type = IOMMU_RESV_RESERVED;
> > +				}
> > +
> > +				region = iommu_alloc_resv_region(start, length, prot, type);
> > +				if (region)
> > +					list_add_tail(&region->list, list);
> > +			}
> > +
> > +			maps += na + ns;
> > +		}
> > +	}
> > +#endif
> > +}
> > +EXPORT_SYMBOL(of_iommu_get_resv_regions);
> > diff --git a/include/linux/of_iommu.h b/include/linux/of_iommu.h
> > index 55c1eb300a86..9a5e6b410dd2 100644
> > --- a/include/linux/of_iommu.h
> > +++ b/include/linux/of_iommu.h
> > @@ -12,6 +12,9 @@ extern const struct iommu_ops *of_iommu_configure(struct device *dev,
> >   					struct device_node *master_np,
> >   					const u32 *id);
> > +extern void of_iommu_get_resv_regions(struct device *dev,
> > +				      struct list_head *list);
> > +
> >   #else
> >   static inline const struct iommu_ops *of_iommu_configure(struct device *dev,
> > @@ -21,6 +24,11 @@ static inline const struct iommu_ops *of_iommu_configure(struct device *dev,
> >   	return NULL;
> >   }
> > +static inline void of_iommu_get_resv_regions(struct device *dev,
> > +					     struct list_head *list)
> > +{
> > +}
> > +
> >   #endif	/* CONFIG_OF_IOMMU */
> >   #endif /* __OF_IOMMU_H */

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