RE: [PATCH v1 1/2] vfio:iommu: Use capabilities do report IOMMU informations

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
> Sent: 09 January 2019 15:37
> To: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> walling@xxxxxxxxxxxxx; cohuck@xxxxxxxxxx; david@xxxxxxxxxx;
> pasic@xxxxxxxxxxxxx; thuth@xxxxxxxxxx; Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@xxxxxxxxxx>
> Subject: Re: [PATCH v1 1/2] vfio:iommu: Use capabilities do report IOMMU
> informations
> 
> On Wed,  9 Jan 2019 13:41:53 +0100
> Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:
> 
> > We add a new flag, VFIO_IOMMU_INFO_CAPABILITIES, inside the
> > vfio_iommu_type1_info to specify the support for capabilities.
> >
> > We add a new capability, with id VFIO_IOMMU_INFO_CAP_DMA
> > in the capability list of the VFIO_IOMMU_GET_INFO ioctl.
> >
> > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > ---
> >  include/uapi/linux/vfio.h | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > index 8131028..54c4fcb 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -669,6 +669,15 @@ struct vfio_iommu_type1_info {
> >  	__u32	flags;
> >  #define VFIO_IOMMU_INFO_PGSIZES (1 << 0)	/* supported page sizes
> info */
> >  	__u64	iova_pgsizes;		/* Bitmap of supported page sizes */
> > +#define VFIO_IOMMU_INFO_CAPABILITIES (1 << 1)  /* support capabilities
> info */
> > +	__u64   cap_offset;     /* Offset within info struct of first cap */
> > +};
> > +
> > +#define VFIO_IOMMU_INFO_CAP_DMA 1
> > +struct vfio_iommu_cap_dma {
> > +	struct vfio_info_cap_header header;
> > +	__u64   dma_start;
> > +	__u64   dma_end;
> >  };
> >
> >  #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
> 
> Unfortunately for most systems, a simple start and end is not really
> sufficient to describe the available IOVA space, there are often
> reserved regions intermixed, so this is not really a complete
> solution.  Shameer tried to solve this last year[1] but we ran into a
> road block that Intel IGD devices impose a reserved range of IOVA
> spaces reported to the user that conflict with existing assignment of
> this device and we haven't figured out yet how to be more selective of
> the enforcement of those reserved ranges.  Thanks,

Right. I had further discussions to unblock this at KVM forum/off-list with
Intel folks and was promised some help.

IIRC the discussion was at, Kevin/Ashok will take another look on your
proposed approach to exclude the RMRR[1] and see whether that is good
enough or not.

Kevin/Ashok,

Please update if you had a chance to look into it.

Thanks,
Shameer

[1]. https://lkml.org/lkml/2018/6/5/897

> Alex
> 
> [1] https://lkml.org/lkml/2018/4/18/293