Re: [PATCH v14 Kernel 3/7] vfio iommu: Add ioctl definition for dirty pages tracking.

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 19 Mar 2020 01:11:10 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> IOMMU container maintains a list of all pages pinned by vfio_pin_pages API.
> All pages pinned by vendor driver through this API should be considered as
> dirty during migration. When container consists of IOMMU capable device and
> all pages are pinned and mapped, then all pages are marked dirty.
> Added support to start/stop pinned and unpinned pages tracking and to get
> bitmap of all dirtied pages for requested IO virtual address range.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> Reviewed-by: Neo Jia <cjia@nvidia.com>
> ---
>  include/uapi/linux/vfio.h | 55 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 55 insertions(+)
> 
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index d0021467af53..043e9eafb255 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -995,6 +995,12 @@ struct vfio_iommu_type1_dma_map {
>  
>  #define VFIO_IOMMU_MAP_DMA _IO(VFIO_TYPE, VFIO_BASE + 13)
>  
> +struct vfio_bitmap {
> +	__u64        pgsize;	/* page size for bitmap */
> +	__u64        size;	/* in bytes */
> +	__u64 __user *data;	/* one bit per page */
> +};
> +
>  /**
>   * VFIO_IOMMU_UNMAP_DMA - _IOWR(VFIO_TYPE, VFIO_BASE + 14,
>   *							struct vfio_dma_unmap)
> @@ -1021,6 +1027,55 @@ struct vfio_iommu_type1_dma_unmap {
>  #define VFIO_IOMMU_ENABLE	_IO(VFIO_TYPE, VFIO_BASE + 15)
>  #define VFIO_IOMMU_DISABLE	_IO(VFIO_TYPE, VFIO_BASE + 16)
>  
> +/**
> + * VFIO_IOMMU_DIRTY_PAGES - _IOWR(VFIO_TYPE, VFIO_BASE + 17,
> + *                                     struct vfio_iommu_type1_dirty_bitmap)
> + * IOCTL is used for dirty pages tracking. Caller sets argsz, which is size of
> + * struct vfio_iommu_type1_dirty_bitmap. Caller set flag depend on which
> + * operation to perform, details as below:
> + *
> + * When IOCTL is called with VFIO_IOMMU_DIRTY_PAGES_FLAG_START set, indicates
> + * migration is active and IOMMU module should track pages which are pinned and
> + * could be dirtied by device.

"...should track" pages dirtied or potentially dirtied by devices.

As soon as we add support for Yan's DMA r/w the pinning requirement is
gone, besides pinning is an in-kernel implementation detail, the user
of this interface doesn't know or care which pages are pinned.

> + * Dirty pages are tracked until tracking is stopped by user application by
> + * setting VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP flag.
> + *
> + * When IOCTL is called with VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP set, indicates
> + * IOMMU should stop tracking pinned pages.

s/pinned/dirtied/

> + *
> + * When IOCTL is called with VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP flag set,
> + * IOCTL returns dirty pages bitmap for IOMMU container during migration for
> + * given IOVA range. User must provide data[] as the structure
> + * vfio_iommu_type1_dirty_bitmap_get through which user provides IOVA range and
> + * pgsize. This interface supports to get bitmap of smallest supported pgsize
> + * only and can be modified in future to get bitmap of specified pgsize.
> + * User must allocate memory for bitmap, zero the bitmap memory and set size
> + * of allocated memory in bitmap_size field. One bit is used to represent one
> + * page consecutively starting from iova offset. User should provide page size
> + * in 'pgsize'. Bit set in bitmap indicates page at that offset from iova is
> + * dirty. Caller must set argsz including size of structure
> + * vfio_iommu_type1_dirty_bitmap_get.
> + *
> + * Only one flag should be set at a time.

"Only one of the flags _START, _STOP, and _GET maybe be specified at a
time."  IOW, let's not presume what yet undefined flags may do.
Hopefully this addresses Dave's concern.

> + *
> + */
> +struct vfio_iommu_type1_dirty_bitmap {
> +	__u32        argsz;
> +	__u32        flags;
> +#define VFIO_IOMMU_DIRTY_PAGES_FLAG_START	(1 << 0)
> +#define VFIO_IOMMU_DIRTY_PAGES_FLAG_STOP	(1 << 1)
> +#define VFIO_IOMMU_DIRTY_PAGES_FLAG_GET_BITMAP	(1 << 2)
> +	__u8         data[];
> +};
> +
> +struct vfio_iommu_type1_dirty_bitmap_get {
> +	__u64              iova;	/* IO virtual address */
> +	__u64              size;	/* Size of iova range */
> +	struct vfio_bitmap bitmap;
> +};
> +
> +#define VFIO_IOMMU_DIRTY_PAGES             _IO(VFIO_TYPE, VFIO_BASE + 17)
> +
>  /* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU -------- */
>  
>  /*