Re: [Qemu-devel] [PATCH 1/1] vfio iommu type1: set size to PAGE_SIZE while looking for iova in dma list

[Kirti Wankhede]

On 12/6/2016 4:24 AM, Alex Williamson wrote:
> On Tue, 6 Dec 2016 02:38:01 +0530
> Kirti Wankhede <address@hidden> wrote:
> 
>> In the functions of pin_pages/unpin_pages from mdev vendor driver,
>> vfio_find_dma() should be called with size as PAGE_SIZE instead of 0.
>> vfio_find_dma() searches for the range in dma_list.
>>
>> In vfio_dma_do_unmap(), vfio_find_dma() when used to look for start
>> address of unmap->iova, size should be 1, not 0. Otherwise vfio_find_dma()
>> returns NULL.
> 
> Hi Kirti,
> 
> I'd prefer to fix the preexisting case of this issue as a separate
> patch, we might want to backport it for stable trees separately from the
> new cases introduced with mdev.  It would also be great if we could go
> into some detail about why size=0 doesn't work in these cases, ie.
> vfio_find_dma() accounting for the end address of the range makes it
> fall through at the wrong branch point.  For the case of the
> preexisting issue, it would also be useful to mention that the other
> case of passing size=0 works correctly due to the -1 in the start
> address calculation.  Finally, I think I agree with your choice to use
> PAGE_SIZE in one case and 1 in the preexisting case, but perhaps we
> could spell that out as one is related to a page size interface and the
> other is trying to test boundary conditions.  Thanks,
> 

Thanks Alex,

Actual problem here is: vfio_dma keeps track of address range from
(dma->iova + 0) to (dma->iova + dma->size - 1), while vfio_find_dma()
search logic looks for range from (dma->iova + 1) to (dma->iova +
dma->size). So either we have to fix the size argument send to
vfio_find_dma() or we have to fix rb-tree creation and search logic.
I took the former path here. I'll add this detail in commit description
and split it as you mentioned above.

Thanks,
Kirti

> Alex
> 
>> Signed-off-by: Kirti Wankhede <address@hidden>
>> Signed-off-by: Neo Jia <address@hidden>
>> Change-Id: Iee6fd45441c342b5e8626087046b2e0075d19a08
>> ---
>>  drivers/vfio/vfio_iommu_type1.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c 
>> b/drivers/vfio/vfio_iommu_type1.c
>> index a28fbddb505c..023fba7b8d5a 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -581,7 +581,7 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
>>              struct vfio_pfn *vpfn;
>>  
>>              iova = user_pfn[i] << PAGE_SHIFT;
>> -            dma = vfio_find_dma(iommu, iova, 0);
>> +            dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
>>              if (!dma) {
>>                      ret = -EINVAL;
>>                      goto pin_unwind;
>> @@ -622,7 +622,7 @@ pin_unwind:
>>              dma_addr_t iova;
>>  
>>              iova = user_pfn[j] << PAGE_SHIFT;
>> -            dma = vfio_find_dma(iommu, iova, 0);
>> +            dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
>>              vfio_unpin_page_external(dma, iova, do_accounting);
>>              phys_pfn[j] = 0;
>>      }
>> @@ -659,7 +659,7 @@ static int vfio_iommu_type1_unpin_pages(void *iommu_data,
>>              dma_addr_t iova;
>>  
>>              iova = user_pfn[i] << PAGE_SHIFT;
>> -            dma = vfio_find_dma(iommu, iova, 0);
>> +            dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
>>              if (!dma)
>>                      goto unpin_exit;
>>              vfio_unpin_page_external(dma, iova, do_accounting);
>> @@ -826,7 +826,7 @@ again:
>>       * mappings within the range.
>>       */
>>      if (iommu->v2) {
>> -            dma = vfio_find_dma(iommu, unmap->iova, 0);
>> +            dma = vfio_find_dma(iommu, unmap->iova, 1);
>>              if (dma && dma->iova != unmap->iova) {
>>                      ret = -EINVAL;
>>                      goto unlock;
>