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SubjectRe: [PATCH v5 2/3] iommu/dma: Reserve IOVA for PCIe inaccessible DMA address
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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@broadcom.com>
>> Based-on-patch-by: Oza Pawandeep <oza.oza@broadcom.com>
>> Reviewed-by: Oza Pawandeep <poza@codeaurora.org>
>> Acked-by: Robin Murphy <robin.murphy@arm.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 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(...);

here, plus commenting the definition of pci_host_bridge::dma_ranges that
it must be sorted in ascending order?

[ 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. ]

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.

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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