[PATCH v8 3/5] iommu/of: Add msi address regions reservation helper

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Marc Zyngier [mailto:marc.zyngier at arm.com]
> Sent: Wednesday, October 04, 2017 12:22 PM
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi at huawei.com>;
> lorenzo.pieralisi at arm.com; sudeep.holla at arm.com; will.deacon at arm.com;
> robin.murphy at arm.com; joro at 8bytes.org; mark.rutland at arm.com;
> robh at kernel.org
> Cc: Gabriele Paoloni <gabriele.paoloni at huawei.com>; John Garry
> <john.garry at huawei.com>; iommu at lists.linux-foundation.org; linux-arm-
> kernel at lists.infradead.org; linux-acpi at vger.kernel.org;
> devicetree at vger.kernel.org; devel at acpica.org; Linuxarm
> <linuxarm at huawei.com>; Wangzhou (B) <wangzhou1 at hisilicon.com>;
> Guohanjun (Hanjun Guo) <guohanjun at huawei.com>
> Subject: Re: [PATCH v8 3/5] iommu/of: Add msi address regions reservation
> helper
> 
> On 27/09/17 14:32, Shameer Kolothum wrote:
> > From: John Garry <john.garry at huawei.com>
> >
> > On some platforms msi-controller address regions have to be excluded
> > from normal IOVA allocation in that they are detected and decoded in a
> > HW specific way by system components and so they cannot be considered
> > normal IOVA address space.
> >
> > Add a helper function that retrieves msi address regions through
> > device tree msi mapping, so that these regions will not be translated
> > by IOMMU and will be excluded from IOVA allocations.
> >
> > Signed-off-by: John Garry <john.garry at huawei.com>
> > [Shameer: Modified msi-parent retrieval logic]
> > Signed-off-by: Shameer Kolothum
> <shameerali.kolothum.thodi at huawei.com>
> > ---
> >  drivers/iommu/of_iommu.c | 95
> > ++++++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/of_iommu.h | 10 +++++
> >  2 files changed, 105 insertions(+)
> >
> > diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index
> > e60e3db..ffd7fb7 100644
> > --- a/drivers/iommu/of_iommu.c
> > +++ b/drivers/iommu/of_iommu.c
> > @@ -21,6 +21,7 @@
> >  #include <linux/iommu.h>
> >  #include <linux/limits.h>
> >  #include <linux/of.h>
> > +#include <linux/of_address.h>
> >  #include <linux/of_iommu.h>
> >  #include <linux/of_pci.h>
> >  #include <linux/slab.h>
> > @@ -138,6 +139,14 @@ static int of_iommu_xlate(struct device *dev,
> >  	return ops->of_xlate(dev, iommu_spec);  }
> >
> > +static int __get_pci_rid(struct pci_dev *pdev, u16 alias, void *data)
> > +{
> > +	u32 *rid = data;
> > +
> > +	*rid = alias;
> > +	return 0;
> > +}
> > +
> >  struct of_pci_iommu_alias_info {
> >  	struct device *dev;
> >  	struct device_node *np;
> > @@ -163,6 +172,73 @@ static int of_pci_iommu_init(struct pci_dev *pdev,
> u16 alias, void *data)
> >  	return info->np == pdev->bus->dev.of_node;  }
> >
> > +static int of_iommu_alloc_resv_region(struct device_node *np,
> > +				      struct list_head *head)
> > +{
> > +	int prot = IOMMU_WRITE | IOMMU_NOEXEC | IOMMU_MMIO;
> > +	struct iommu_resv_region *region;
> > +	struct resource res;
> > +	int err;
> > +
> > +	err = of_address_to_resource(np, 0, &res);
> 
> What is the rational for registering the first region only? Surely you can have
> more than one region in an MSI controller (yes, your particular case is the ITS
> which has only one, but we're trying to do something generic here).

Ok. 

> Another issue I have with this code is that it inserts all of the ITS MMIO in the
> RESV_MSI range. As long as we don't generate any page tables for this, we're
> fine. But if we ever change this, we'll end-up with the ITS programming
> interface being exposed to a device, which wouldn't be acceptable.

I understand the concern of reserving the whole of ITS MMIO region. Sorry, 
but just being curious, how this will be exposed to a  device ? You mean a device
can  be configured to access the ITS MMIO region and it will fail because there is
no SMMU mapping for that?
 
> Why can't we have some generic property instead, that would describe the
> actual ranges that cannot be translated? That way, no random insertion of a
> random range, and relatively future proof.
> 
> I'm not sure where to declare it (PCIe node? IOMMU node?), but it'd feel like
> a much nicer and simpler solution to this problem.

I am not sure that will be seen as legitimizing the untranslated regions or not.
We had this discussion to include the regions specified in IORT spec and the
answer was that, it will in a way legitimize this and encourage future
implementations.

How about making the _msi_get_resv_regions() function be very specific to GIC
ITS like _its_msi_get_resv_regions() ? Is that something we can consider?
(In fact we had a checking for "arm, gic-v3-its" in a previous version of this series).

Thanks,
Shameer