Re: [PATCH v5 2/3] iommu/dma: Reserve IOVA for PCIe inaccessible DMA address

[Lorenzo Pieralisi]

On Fri, May 03, 2019 at 10:53:23AM +0530, Srinath Mannam wrote:
> Hi Robin, Lorenzo,
> 
> Thanks for review and guidance.
> AFAIU, conclusion of discussion is, to return error if dma-ranges list
> is not sorted.
> 
> So that, Can I send a new patch with below change to return error if
> dma-ranges list is not sorted?

You can but I can't guarantee it will make it for v5.2.

We will have to move the DT parsing and dma list ranges creation
to core code anyway because I want this to work by construction,
so even if we manage to make v5.2 you will have to do that.

I pushed a branch out:

not-to-merge/iova-dma-ranges

where I rewrote all commit logs and I am not willing to do it again
so please use them for your v6 posting if you manage to make it
today.

Lorenzo

> -static void iova_reserve_pci_windows(struct pci_dev *dev,
> +static int iova_reserve_pci_windows(struct pci_dev *dev,
>                 struct iova_domain *iovad)
>  {
>         struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
> @@ -227,11 +227,15 @@ static void iova_reserve_pci_windows(struct pci_dev *dev,
>         resource_list_for_each_entry(window, &bridge->dma_ranges) {
>                 end = window->res->start - window->offset;
>  resv_iova:
> -               if (end - start) {
> +               if (end > start) {
>                         lo = iova_pfn(iovad, start);
>                         hi = iova_pfn(iovad, end);
>                         reserve_iova(iovad, lo, hi);
> +               } else {
> +                       dev_err(&dev->dev, "Unsorted dma_ranges list\n");
> +                       return -EINVAL;
>                 }
> +
> 
> Please provide your inputs if any more changes required. Thank you,
> 
> Regards,
> Srinath.
> 
> On Thu, May 2, 2019 at 7:45 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
> >
> > On 02/05/2019 14:06, Lorenzo Pieralisi wrote:
> > > On Thu, May 02, 2019 at 12:27:02PM +0100, Robin Murphy wrote:
> > >> Hi Lorenzo,
> > >>
> > >> On 02/05/2019 12:01, Lorenzo Pieralisi wrote:
> > >>> On Wed, May 01, 2019 at 11:06:25PM +0530, Srinath Mannam wrote:
> > >>>> dma_ranges field of PCI host bridge structure has resource entries in
> > >>>> sorted order of address range given through dma-ranges DT property. This
> > >>>> list is the accessible DMA address range. So that this resource list will
> > >>>> be processed and reserve IOVA address to the inaccessible address holes in
> > >>>> the list.
> > >>>>
> > >>>> This method is similar to PCI IO resources address ranges reserving in
> > >>>> IOMMU for each EP connected to host bridge.
> > >>>>
> > >>>> Signed-off-by: Srinath Mannam <srinath.mannam@xxxxxxxxxxxx>
> > >>>> Based-on-patch-by: Oza Pawandeep <oza.oza@xxxxxxxxxxxx>
> > >>>> Reviewed-by: Oza Pawandeep <poza@xxxxxxxxxxxxxx>
> > >>>> Acked-by: Robin Murphy <robin.murphy@xxxxxxx>
> > >>>> ---
> > >>>>    drivers/iommu/dma-iommu.c | 19 +++++++++++++++++++
> > >>>>    1 file changed, 19 insertions(+)
> > >>>>
> > >>>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > >>>> index 77aabe6..da94844 100644
> > >>>> --- a/drivers/iommu/dma-iommu.c
> > >>>> +++ b/drivers/iommu/dma-iommu.c
> > >>>> @@ -212,6 +212,7 @@ static void iova_reserve_pci_windows(struct pci_dev *dev,
> > >>>>            struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
> > >>>>            struct resource_entry *window;
> > >>>>            unsigned long lo, hi;
> > >>>> +  phys_addr_t start = 0, end;
> > >>>>            resource_list_for_each_entry(window, &bridge->windows) {
> > >>>>                    if (resource_type(window->res) != IORESOURCE_MEM)
> > >>>> @@ -221,6 +222,24 @@ static void iova_reserve_pci_windows(struct pci_dev *dev,
> > >>>>                    hi = iova_pfn(iovad, window->res->end - window->offset);
> > >>>>                    reserve_iova(iovad, lo, hi);
> > >>>>            }
> > >>>> +
> > >>>> +  /* Get reserved DMA windows from host bridge */
> > >>>> +  resource_list_for_each_entry(window, &bridge->dma_ranges) {
> > >>>
> > >>> If this list is not sorted it seems to me the logic in this loop is
> > >>> broken and you can't rely on callers to sort it because it is not a
> > >>> written requirement and it is not enforced (you know because you
> > >>> wrote the code but any other developer is not supposed to guess
> > >>> it).
> > >>>
> > >>> Can't we rewrite this loop so that it does not rely on list
> > >>> entries order ?
> > >>
> > >> The original idea was that callers should be required to provide a sorted
> > >> list, since it keeps things nice and simple...
> > >
> > > I understand, if it was self-contained in driver code that would be fine
> > > but in core code with possible multiple consumers this must be
> > > documented/enforced, somehow.
> > >
> > >>> I won't merge this series unless you sort it, no pun intended.
> > >>>
> > >>> Lorenzo
> > >>>
> > >>>> +          end = window->res->start - window->offset;
> > >>
> > >> ...so would you consider it sufficient to add
> > >>
> > >>              if (end < start)
> > >>                      dev_err(...);
> > >
> > > We should also revert any IOVA reservation we did prior to this
> > > error, right ?
> >
> > I think it would be enough to propagate an error code back out through
> > iommu_dma_init_domain(), which should then end up aborting the whole
> > IOMMU setup - reserve_iova() isn't really designed to be undoable, but
> > since this is the kind of error that should only ever be hit during
> > driver or DT development, as long as we continue booting such that the
> > developer can clearly see what's gone wrong, I don't think we need
> > bother spending too much effort tidying up inside the unused domain.
> >
> > > Anyway, I think it is best to ensure it *is* sorted.
> > >
> > >> here, plus commenting the definition of pci_host_bridge::dma_ranges
> > >> that it must be sorted in ascending order?
> > >
> > > I don't think that commenting dma_ranges would help much, I am more
> > > keen on making it work by construction.
> > >
> > >> [ I guess it might even make sense to factor out the parsing and list
> > >> construction from patch #3 into an of_pci core helper from the beginning, so
> > >> that there's even less chance of another driver reimplementing it
> > >> incorrectly in future. ]
> > >
> > > This makes sense IMO and I would like to take this approach if you
> > > don't mind.
> >
> > Sure - at some point it would be nice to wire this up to
> > pci-host-generic for Juno as well (with a parallel version for ACPI
> > _DMA), so from that viewpoint, the more groundwork in place the better :)
> >
> > Thanks,
> > Robin.
> >
> > >
> > > Either this or we move the whole IOVA reservation and dma-ranges
> > > parsing into PCI IProc.
> > >
> > >> Failing that, although I do prefer the "simple by construction"
> > >> approach, I'd have no objection to just sticking a list_sort() call in
> > >> here instead, if you'd rather it be entirely bulletproof.
> > >
> > > I think what you outline above is a sensible way forward - if we
> > > miss the merge window so be it.
> > >
> > > Thanks,
> > > Lorenzo
> > >
> > >> Robin.
> > >>
> > >>>> +resv_iova:
> > >>>> +          if (end - start) {
> > >>>> +                  lo = iova_pfn(iovad, start);
> > >>>> +                  hi = iova_pfn(iovad, end);
> > >>>> +                  reserve_iova(iovad, lo, hi);
> > >>>> +          }
> > >>>> +          start = window->res->end - window->offset + 1;
> > >>>> +          /* If window is last entry */
> > >>>> +          if (window->node.next == &bridge->dma_ranges &&
> > >>>> +              end != ~(dma_addr_t)0) {
> > >>>> +                  end = ~(dma_addr_t)0;
> > >>>> +                  goto resv_iova;
> > >>>> +          }
> > >>>> +  }
> > >>>>    }
> > >>>>    static int iova_reserve_iommu_regions(struct device *dev,
> > >>>> --
> > >>>> 2.7.4
> > >>>>