Re: [PATCH 2/3] iommu/pci: reserve iova for PCI masters

[Oza Oza]

On Fri, May 5, 2017 at 9:21 PM, Robin Murphy <robin.murphy@xxxxxxx> wrote:
> On 04/05/17 19:52, Oza Oza wrote:
>> On Thu, May 4, 2017 at 11:50 PM, Robin Murphy <robin.murphy@xxxxxxx> wrote:
>>> On 03/05/17 05:46, Oza Pawandeep wrote:
>>>> this patch reserves the iova for PCI masters.
>>>> ARM64 based SOCs may have scattered memory banks.
>>>> such as iproc based SOC has
>>>>
>>>> <0x00000000 0x80000000 0x0 0x80000000>, /* 2G @ 2G */
>>>> <0x00000008 0x80000000 0x3 0x80000000>, /* 14G @ 34G */
>>>> <0x00000090 0x00000000 0x4 0x00000000>, /* 16G @ 576G */
>>>> <0x000000a0 0x00000000 0x4 0x00000000>; /* 16G @ 640G */
>>>>
>>>> but incoming PCI transcation addressing capability is limited
>>>> by host bridge, for example if max incoming window capability
>>>> is 512 GB, then 0x00000090 and 0x000000a0 will fall beyond it.
>>>>
>>>> to address this problem, iommu has to avoid allocating iovas which
>>>> are reserved. which inturn does not allocate iova if it falls into hole.
>>>
>>> I don't necessarily disagree with doing this, as we could do with facing
>>> up to the issue of discontiguous DMA ranges in particular (I too have a
>>> platform with this problem), but I'm still not overly keen on pulling DT
>>> specifics into this layer. More than that, though, if we are going to do
>>> it, then we should do it for all devices with a restrictive
>>> "dma-ranges", not just PCI ones.
>>>
>>
>> How do you propose to do it ?
>>
>> my thinking is this:
>> iova_reserve_pci_windows is written specific for PCI, and I am adding there.
>>
>> ideally
>> struct pci_host_bridge should have new member:
>>
>> struct list_head inbound_windows; /* resource_entry */
>>
>> but somehow this resource have to be filled much before
>> iommu_dma_init_domain happens.
>> and use brdge resource directly in iova_reserve_pci_windows as it is
>> already doing it for outbound memory.
>>
>> this will detach the DT specifics from dma-immu layer.
>> let me know how this sounds.
>
> Please check the state of the code currently queued in Joerg's tree and
> in linux-next - iommu_dma_get_resv_regions() has room for
> device-agnostic stuff before the if (!dev_is_pci(dev)) check.
>
> Furthermore, with the probe-deferral changes we end up with a common
> dma_configure() routine to abstract the firmware-specifics of
> of_dma_configure() vs. acpi_dma_configure(), so it would make sense to
> give drivers etc. a similar interface for interrogating ranges. i.e.
> some common function that abstracts the difference between parsing DT
> dma-ranges vs. the ACPI _DMA object, either with a list-based get/put
> model or perhaps an iterator with a user-provided callback (so users
> could process in-place or create their own list as necessary). Unless of
> course we go all the way to making the ranges an inherent part of the
> device layer like some MIPS platforms currently do.
>
> Robin.
>

Hi Robin,

your above comments are taken care to the best of my understanding.
Kindly have a look at the PATCH v7.
the whole patch-set takes care of IOVA reservation for PCI inbound memory.
now there is no dependency on IOMMU and OF layer.

Regards,
Oza.


>>>> Bug: SOC-5216
>>>> Change-Id: Icbfc99a045d730be143fef427098c937b9d46353
>>>> Signed-off-by: Oza Pawandeep <oza.oza@xxxxxxxxxxxx>
>>>> Reviewed-on: http://gerrit-ccxsw.broadcom.net/40760
>>>> Reviewed-by: vpx_checkpatch status <vpx_checkpatch@xxxxxxxxxxxx>
>>>> Reviewed-by: CCXSW <ccxswbuild@xxxxxxxxxxxx>
>>>> Tested-by: vpx_autobuild status <vpx_autobuild@xxxxxxxxxxxx>
>>>> Tested-by: vpx_smoketest status <vpx_smoketest@xxxxxxxxxxxx>
>>>> Tested-by: CCXSW <ccxswbuild@xxxxxxxxxxxx>
>>>> Reviewed-by: Scott Branden <scott.branden@xxxxxxxxxxxx>
>>>>
>>>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
>>>> index 48d36ce..08764b0 100644
>>>> --- a/drivers/iommu/dma-iommu.c
>>>> +++ b/drivers/iommu/dma-iommu.c
>>>> @@ -27,6 +27,7 @@
>>>>  #include <linux/iova.h>
>>>>  #include <linux/irq.h>
>>>>  #include <linux/mm.h>
>>>> +#include <linux/of_pci.h>
>>>>  #include <linux/pci.h>
>>>>  #include <linux/scatterlist.h>
>>>>  #include <linux/vmalloc.h>
>>>> @@ -171,8 +172,12 @@ static void iova_reserve_pci_windows(struct pci_dev *dev,
>>>>               struct iova_domain *iovad)
>>>>  {
>>>>       struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
>>>> +     struct device_node *np = bridge->dev.parent->of_node;
>>>>       struct resource_entry *window;
>>>>       unsigned long lo, hi;
>>>> +     int ret;
>>>> +     dma_addr_t tmp_dma_addr = 0, dma_addr;
>>>> +     LIST_HEAD(res);
>>>>
>>>>       resource_list_for_each_entry(window, &bridge->windows) {
>>>>               if (resource_type(window->res) != IORESOURCE_MEM &&
>>>> @@ -183,6 +188,36 @@ static void iova_reserve_pci_windows(struct pci_dev *dev,
>>>>               hi = iova_pfn(iovad, window->res->end - window->offset);
>>>>               reserve_iova(iovad, lo, hi);
>>>>       }
>>>> +
>>>> +     /* PCI inbound memory reservation. */
>>>> +     ret = of_pci_get_dma_ranges(np, &res);
>>>> +     if (!ret) {
>>>> +             resource_list_for_each_entry(window, &res) {
>>>> +                     struct resource *res_dma = window->res;
>>>> +
>>>> +                     dma_addr = res_dma->start - window->offset;
>>>> +                     if (tmp_dma_addr > dma_addr) {
>>>> +                             pr_warn("PCI: failed to reserve iovas; ranges should be sorted\n");
>>>
>>> I don't see anything in the DT spec about the entries having to be
>>> sorted, and it's not exactly impossible to sort a list if you need it so
>>> (and if I'm being really pedantic, one could still trigger this with a
>>> list that *is* sorted, only by different criteria).
>>>
>>
>> we have to sort it the way we want then. I can make it sort then.
>> thanks for the suggestion.
>>
>>> Robin.
>>>
>>>> +                             return;
>>>> +                     }
>>>> +                     if (tmp_dma_addr != dma_addr) {
>>>> +                             lo = iova_pfn(iovad, tmp_dma_addr);
>>>> +                             hi = iova_pfn(iovad, dma_addr - 1);
>>>> +                             reserve_iova(iovad, lo, hi);
>>>> +                     }
>>>> +                     tmp_dma_addr = window->res->end - window->offset;
>>>> +             }
>>>> +             /*
>>>> +              * the last dma-range should honour based on the
>>>> +              * 32/64-bit dma addresses.
>>>> +              */
>>>> +             if (tmp_dma_addr < DMA_BIT_MASK(sizeof(dma_addr_t) * 8)) {
>>>> +                     lo = iova_pfn(iovad, tmp_dma_addr);
>>>> +                     hi = iova_pfn(iovad,
>>>> +                                   DMA_BIT_MASK(sizeof(dma_addr_t) * 8) - 1);
>>>> +                     reserve_iova(iovad, lo, hi);
>>>> +             }
>>>> +     }
>>>>  }
>>>>
>>>>  /**
>>>>
>>>
>