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

[Kirti Wankhede]

On 3/31/2020 2:28 AM, Alex Williamson wrote:
> On Mon, 30 Mar 2020 22:20:43 +0530
> Kirti Wankhede <address@hidden> wrote:
>
> > Flag VFIO_IOMMU_INFO_DIRTY_PGS in VFIO_IOMMU_GET_INFO indicates that driver
> > support dirty pages tracking.
> >
> > Signed-off-by: Kirti Wankhede <address@hidden>
> > Reviewed-by: Neo Jia <address@hidden>
> > ---
> >   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