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SubjectRe: [PATCH v2] vfio iommu: Add dma available capability
On Mon, 14 Sep 2020 18:25:31 -0400
Matthew Rosato <mjrosato@linux.ibm.com> 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@linux.ibm.com>
> ---
> 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..." ?

> + *
> + * 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."

?

> + */
> +#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)
>
> /**

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