Re: [Qemu-devel] [PATCH v3 3/3] vfio: Fix 128 bit handling

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 08/29/2013 01:18 AM, Alex Williamson wrote:
> On Thu, 2013-08-22 at 21:29 +1000, Alexey Kardashevskiy wrote:
>> Upcoming VFIO on SPAPR PPC64 support will initialize the IOMMU
>> memory region with UINT64_MAX (2^64 bytes) size so int128_get64()
>> will assert.
>>
>> The patch takes care of this check. The existing type1 IOMMU code
>> is not expected to map all 64 bits of RAM so the patch does not
>> touch that part.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> ---
>> Changes:
>> v2:
>> * used new function int128_exts64()
>> ---
>>  hw/misc/vfio.c | 11 ++++++++---
>>  1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
>> index dfe3a80..3878fc7 100644
>> --- a/hw/misc/vfio.c
>> +++ b/hw/misc/vfio.c
>> @@ -1920,6 +1920,7 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>      VFIOContainer *container = container_of(listener, VFIOContainer,
>>                                              iommu_data.listener);
>>      hwaddr iova, end;
>> +    Int128 llend;
>>      void *vaddr;
>>      int ret;
>>  
>> @@ -1940,13 +1941,17 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>      }
>>  
>>      iova = TARGET_PAGE_ALIGN(section->offset_within_address_space);
>> -    end = (section->offset_within_address_space + int128_get64(section->size)) &
>> -          TARGET_PAGE_MASK;
>> +    llend = int128_make64(section->offset_within_address_space);
>> +    llend = int128_add(llend, section->size);
>> +    llend = int128_and(llend, int128_exts64(TARGET_PAGE_MASK));
>>  
>> -    if (iova >= end) {
>> +    if (int128_ge(int128_make64(iova), llend)) {
>>          return;
>>      }
>>  
>> +    end = (section->offset_within_address_space + int128_get64(section->size)) &
>> +          TARGET_PAGE_MASK;
>> +
> 
> I'm confused, we build an Int128 version of end above for the
> comparison, why isn't this just:
> 
> end = int128_get64(llend);


section->size for IOMMU memory region I have on spapr-vfio is 2^64 so
int128_get64() fails.


> here?  Thanks,
> 
> Alex
> 
>>      vaddr = memory_region_get_ram_ptr(section->mr) +
>>              section->offset_within_region +
>>              (iova - section->offset_within_address_space);
> 
> 
> 


-- 
Alexey