Re: [PATCH v2] vfio iommu: Add dma available capability

[Matthew Rosato]

On 9/15/20 5:44 AM, Cornelia Huck wrote:
> On Mon, 14 Sep 2020 18:25:31 -0400
> Matthew Rosato <mjrosato@xxxxxxxxxxxxx> wrote:
>
> > Commit 492855939bdb ("vfio/type1: Limit DMA mappings per container")
> > added the ability to limit the number of memory backed DMA mappings.
> > However on s390x, when lazy mapping is in use, we use a very large
> > number of concurrent mappings.  Let's provide the current allowable
> > number of DMA mappings to userspace via the IOMMU info chain so that
> > userspace can take appropriate mitigation.
> >
> > Signed-off-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> > ---
> >   drivers/vfio/vfio_iommu_type1.c | 17 +++++++++++++++++
> >   include/uapi/linux/vfio.h       | 16 ++++++++++++++++
> >   2 files changed, 33 insertions(+)
>
> (...)
>
> > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > index 9204705..a8cc4a5 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -1039,6 +1039,22 @@ struct vfio_iommu_type1_info_cap_migration {
> >   	__u64	max_dirty_bitmap_size;		/* in bytes */
> >   };
> >   
> > +/*
> > + * The DMA available capability allows to report the current number of
> > + * simultaneously outstanding DMA mappings that are allowed.
> > + *
> > + * The structures below define version 1 of this capability.
>
> "The structure below defines..." ?

OK

> > + *
> > + * max: specifies the maximum number of outstanding DMA mappings allowed.
>
> I think you forgot to tweak that one:
>
> "avail: specifies the current number of outstanding DMA mappings allowed."
>
> ?

Yep, that's a leftover from v1 :(

> > + */
> > +#define VFIO_IOMMU_TYPE1_INFO_DMA_AVAIL 3
> > +
> > +struct vfio_iommu_type1_info_dma_avail {
> > +	struct	vfio_info_cap_header header;
> > +	__u32	avail;
> > +};
> > +
> > +
> >   #define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)
> >   
> >   /**