Re: [PATCH v17 Kernel 6/7] vfio iommu: Adds flag to indicate dirty pages tracking capability support

[Kirti Wankhede <kwankhede@nvidia.com>]

On 3/31/2020 2:28 AM, Alex Williamson wrote:
> On Mon, 30 Mar 2020 22:20:43 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
> 
>> Flag VFIO_IOMMU_INFO_DIRTY_PGS in VFIO_IOMMU_GET_INFO indicates that driver
>> support dirty pages tracking.
>>
>> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
>> Reviewed-by: Neo Jia <cjia@nvidia.com>
>> ---
>>   drivers/vfio/vfio_iommu_type1.c | 3 ++-
>>   include/uapi/linux/vfio.h       | 5 +++--
>>   2 files changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 266550bd7307..9fe12b425976 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -2390,7 +2390,8 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>>   			info.cap_offset = 0; /* output, no-recopy necessary */
>>   		}
>>   
>> -		info.flags = VFIO_IOMMU_INFO_PGSIZES;
>> +		info.flags = VFIO_IOMMU_INFO_PGSIZES |
>> +			     VFIO_IOMMU_INFO_DIRTY_PGS;
>>   
>>   		info.iova_pgsizes = vfio_pgsize_bitmap(iommu);
>>   
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index e3cbf8b78623..0fe7c9a6f211 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -985,8 +985,9 @@ struct vfio_device_feature {
>>   struct vfio_iommu_type1_info {
>>   	__u32	argsz;
>>   	__u32	flags;
>> -#define VFIO_IOMMU_INFO_PGSIZES (1 << 0)	/* supported page sizes info */
>> -#define VFIO_IOMMU_INFO_CAPS	(1 << 1)	/* Info supports caps */
>> +#define VFIO_IOMMU_INFO_PGSIZES   (1 << 0) /* supported page sizes info */
>> +#define VFIO_IOMMU_INFO_CAPS      (1 << 1) /* Info supports caps */
>> +#define VFIO_IOMMU_INFO_DIRTY_PGS (1 << 2) /* supports dirty page tracking */
>>   	__u64	iova_pgsizes;	/* Bitmap of supported page sizes */
>>   	__u32   cap_offset;	/* Offset within info struct of first cap */
>>   };
> 
> 
> As I just mentioned in my reply to Yan, I'm wondering if
> VFIO_CHECK_EXTENSION would be a better way to expose this.  The
> difference is relatively trivial, but currently the only flag
> set by VFIO_IOMMU_GET_INFO is to indicate the presence of a field in
> the returned structure.  I think this is largely true of other INFO
> ioctls within vfio as well and we're already using the
> VFIO_CHECK_EXTENSION ioctl to check supported IOMMU models, and IOMMU
> cache coherency.  We'd simply need to define a VFIO_DIRTY_PGS_IOMMU
> value (9) and return 1 for that case.  Then when we enable support for
> dirt pages that can span multiple mappings, we can add a v2 extensions,
> or "MULTI" variant of this extension, since it should be backwards
> compatible.
> 
> The v2/multi version will again require that the user provide a zero'd
> bitmap, but I don't think that should be a problem as part of the
> definition of that version (we won't know if the user is using v1 or
> v2, but a v1 user should only retrieve bitmaps that exactly match
> existing mappings, where all bits will be written).  Thanks,
> 
> Alex
> 

I look at these two ioctls as : VFIO_CHECK_EXTENSION is used to get 
IOMMU type, while VFIO_IOMMU_GET_INFO is used to get properties of a 
particular IOMMU type, right?

Then I think VFIO_IOMMU_INFO_DIRTY_PGS should be part of 
VFIO_IOMMU_GET_INFO and when we add code for v2/multi, a flag should be 
added to VFIO_IOMMU_GET_INFO.

Thanks,
Kirti