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

Kirti Wankhede
2020-03-31T19:09:05Z

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