[PATCH 2/2] arm64/dma-mapping: validate dma_masks against IORT defined limits

[Robin Murphy]

On 01/02/17 14:36, Lorenzo Pieralisi wrote:
> On Wed, Feb 01, 2017 at 01:44:02PM +0000, Robin Murphy wrote:
>> Hi Nate,
>>
>> On 31/01/17 20:16, Nate Watterson wrote:
>>> Some drivers set the dma_mask of client devices based solely on values
>>> read from capability registers which may not account for platform
>>> specific bus address width limitations. Fortunately, the ACPI IORT table
>>> provides a way to report the effective number of address bits a device
>>> can use to access memory. This information, when present, is used to
>>> supplement the checks already being done in dma_supported() to avoid
>>> setting overly generous dma_masks.
>>
>> This is equally a problem for DT, and I think in general we'd prefer not
>> to be dragging ACPI/DT specifics in at this level when there's a clean
>> way to address it more generally. There is some recent ongoing
>> discussion and work in this area (latest part at [1]) - I have a local
>> branch somewhere implementing the stricter "don't special case default
>> masks" version (after I came around to Arnd's viewpoint), which I must
>> refresh myself on because there was some anomaly in the core DT code
>> which that brought to light.
> 
> Agreed. I can prototype the ACPI version by using the _DMA object in the
> ACPI specs instead of IORT specific bindings (what to do for named
> components has to be seen given that _DMA object and IORT bindings can
> provide different information - though _DMA object usage at least on x86
> seems non-existent, whether we should use it or not on ARM is still a
> question mark). Anyway, the IORT parsing code in patch 1 is simple, we
> have to decide how to handle the information retrieved. I will have a
> look at [1] let me know if you need help prototyping and testing it with
> ACPI.

Essentially, all that needs to be done is to ensure that the initial
masks set by acpi_dma_configure() truly reflect the maximum hardware
capability; everything else will then just fall out of that. The
aforementioned thing on the DT side is that of_dma_configure() currently
has a bug which prevents masks larger than 32 bits actually being
assigned from "dma-ranges" - I need to split out a proper patch from the
"git commit -am 'hacks'" that I have on this local branch :)

Robin.

> 
> Lorenzo
> 
>>> Signed-off-by: Nate Watterson <nwatters at codeaurora.org>
>>> ---
>>>  arch/arm64/mm/dma-mapping.c | 20 +++++++++++++++++++-
>>>  1 file changed, 19 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
>>> index e040827..467fd23 100644
>>> --- a/arch/arm64/mm/dma-mapping.c
>>> +++ b/arch/arm64/mm/dma-mapping.c
>>> @@ -19,6 +19,7 @@
>>>  
>>>  #include <linux/gfp.h>
>>>  #include <linux/acpi.h>
>>> +#include <linux/acpi_iort.h>
>>>  #include <linux/bootmem.h>
>>>  #include <linux/cache.h>
>>>  #include <linux/export.h>
>>> @@ -347,6 +348,12 @@ static int __swiotlb_get_sgtable(struct device *dev, struct sg_table *sgt,
>>>  
>>>  static int __swiotlb_dma_supported(struct device *hwdev, u64 mask)
>>>  {
>>> +	int dma_limit;
>>> +
>>> +	dma_limit = iort_get_memory_address_limit(hwdev);
>>> +	if (dma_limit >= 0 && DMA_BIT_MASK(dma_limit) < mask)
>>> +		return 0;
>>> +
>>>  	if (swiotlb)
>>>  		return swiotlb_dma_supported(hwdev, mask);
>>>  	return 1;
>>> @@ -784,6 +791,17 @@ static void __iommu_unmap_sg_attrs(struct device *dev,
>>>  	iommu_dma_unmap_sg(dev, sgl, nelems, dir, attrs);
>>>  }
>>>  
>>> +static int __iommu_dma_supported(struct device *hwdev, u64 mask)
>>> +{
>>> +	int dma_limit;
>>> +
>>> +	dma_limit = iort_get_memory_address_limit(hwdev);
>>> +	if (dma_limit >= 0 && DMA_BIT_MASK(dma_limit) < mask)
>>> +		return 0;
>>> +
>>> +	return iommu_dma_supported(hwdev, mask);
>>
>> Either way, this reminds me that iommu_dma_supported() is another thing
>> I got completely wrong - time to write yet another patch...
>>
>> Robin.
>>
>> [1]:http://www.mail-archive.com/linux-renesas-soc@vger.kernel.org/msg10637.html
>>
>>> +}
>>> +
>>>  static struct dma_map_ops iommu_dma_ops = {
>>>  	.alloc = __iommu_alloc_attrs,
>>>  	.free = __iommu_free_attrs,
>>> @@ -799,7 +817,7 @@ static void __iommu_unmap_sg_attrs(struct device *dev,
>>>  	.sync_sg_for_device = __iommu_sync_sg_for_device,
>>>  	.map_resource = iommu_dma_map_resource,
>>>  	.unmap_resource = iommu_dma_unmap_resource,
>>> -	.dma_supported = iommu_dma_supported,
>>> +	.dma_supported = __iommu_dma_supported,
>>>  	.mapping_error = iommu_dma_mapping_error,
>>>  };
>>>  
>>>
>>