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Date:   Fri, 3 May 2019 16:00:39 +0530
From:   Srinath Mannam <srinath.mannam@...adcom.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Eric Auger <eric.auger@...hat.com>,
        Joerg Roedel <joro@...tes.org>, poza@...eaurora.org,
        Ray Jui <rjui@...adcom.com>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 2/3] iommu/dma: Reserve IOVA for PCIe inaccessible DMA address

Hi Robin,


On Fri, May 3, 2019 at 3:58 PM Robin Murphy <robin.murphy@....com> wrote:
>
> On 03/05/2019 06:23, 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?
> >
> > -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,
>
> You also need to handle and return this error where
> iova_reserve_pci_windows() is called from iova_reserve_iommu_regions().
Thank you. I am doing this.

Regards,
Srinath.
>
> Robin.
>
> > Regards,
> > Srinath.
> >
> > On Thu, May 2, 2019 at 7:45 PM Robin Murphy <robin.murphy@....com> 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@...adcom.com>
> >>>>>> Based-on-patch-by: Oza Pawandeep <oza.oza@...adcom.com>
> >>>>>> Reviewed-by: Oza Pawandeep <poza@...eaurora.org>
> >>>>>> Acked-by: Robin Murphy <robin.murphy@....com>
> >>>>>> ---
> >>>>>>     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
> >>>>>>

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