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

From: Robin Murphy
Date: Thu May 02 2019 - 07:27:50 EST

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

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.


+ end = window->res->start - window->offset; would you consider it sufficient to add

if (end < start)

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.


+ 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-> == &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,