Re: [RFC PATCH v5 23/26] util: Add iova_tree_alloc

[Jason Wang]

在 2021/10/30 上午2:35, Eugenio Pérez 写道:
> This iova tree function allows it to look for a hole in allocated
> regions and return a totally new translation for a given translated
> address.
>
> It's usage is mainly to allow devices to access qemu address space,
> remapping guest's one into a new iova space where qemu can add chunks of
> addresses.
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>   include/qemu/iova-tree.h |  17 +++++
>   util/iova-tree.c         | 139 +++++++++++++++++++++++++++++++++++++++
>   2 files changed, 156 insertions(+)
>
> diff --git a/include/qemu/iova-tree.h b/include/qemu/iova-tree.h
> index 8249edd764..33f9b2e13f 100644
> --- a/include/qemu/iova-tree.h
> +++ b/include/qemu/iova-tree.h
> @@ -29,6 +29,7 @@
>   #define  IOVA_OK           (0)
>   #define  IOVA_ERR_INVALID  (-1) /* Invalid parameters */
>   #define  IOVA_ERR_OVERLAP  (-2) /* IOVA range overlapped */
> +#define  IOVA_ERR_NOMEM    (-3) /* Cannot allocate */


I think we need a better name other than "NOMEM", since it's actually 
means there's no sufficient hole for the range?


>   
>   typedef struct IOVATree IOVATree;
>   typedef struct DMAMap {
> @@ -119,6 +120,22 @@ const DMAMap *iova_tree_find_address(const IOVATree *tree, 
> hwaddr iova);
>    */
>   void iova_tree_foreach(IOVATree *tree, iova_tree_iterator iterator);
>   
> +/**
> + * iova_tree_alloc:
> + *
> + * @tree: the iova tree to allocate from
> + * @map: the new map (as translated addr & size) to allocate in iova region
> + * @iova_begin: the minimum address of the allocation
> + * @iova_end: the maximum addressable direction of the allocation
> + *
> + * Allocates a new region of a given size, between iova_min and iova_max.
> + *
> + * Return: Same as iova_tree_insert, but cannot overlap and can be out of
> + * free contiguous range. Caller can get the assigned iova in map->iova.
> + */
> +int iova_tree_alloc(IOVATree *tree, DMAMap *map, hwaddr iova_begin,
> +                    hwaddr iova_end);
> +


"iova_tree_alloc_map" seems better.


>   /**
>    * iova_tree_destroy:
>    *
> diff --git a/util/iova-tree.c b/util/iova-tree.c
> index 23ea35b7a4..27c921c4e2 100644
> --- a/util/iova-tree.c
> +++ b/util/iova-tree.c
> @@ -16,6 +16,36 @@ struct IOVATree {
>       GTree *tree;
>   };
>   
> +/* Args to pass to iova_tree_alloc foreach function. */
> +struct IOVATreeAllocArgs {
> +    /* Size of the desired allocation */
> +    size_t new_size;
> +
> +    /* The minimum address allowed in the allocation */
> +    hwaddr iova_begin;
> +
> +    /* The last addressable allowed in the allocation */
> +    hwaddr iova_last;
> +
> +    /* Previously-to-last iterated map, can be NULL in the first node */
> +    const DMAMap *hole_left;
> +
> +    /* Last iterated map */
> +    const DMAMap *hole_right;


Any reason we can move those to IOVATree structure, it can simplify a 
lot of things.


> +};
> +
> +/**
> + * Iterate args to tne next hole
> + *
> + * @args  The alloc arguments
> + * @next  The next mapping in the tree. Can be NULL to signal the last one
> + */
> +static void iova_tree_alloc_args_iterate(struct IOVATreeAllocArgs *args,
> +                                         const DMAMap *next) {
> +    args->hole_left = args->hole_right;
> +    args->hole_right = next;
> +}
> +
>   static int iova_tree_compare(gconstpointer a, gconstpointer b, gpointer data)
>   {
>       const DMAMap *m1 = a, *m2 = b;
> @@ -107,6 +137,115 @@ int iova_tree_remove(IOVATree *tree, const DMAMap *map)
>       return IOVA_OK;
>   }
>   
> +/**
> + * Try to accomodate a map of size ret->size in a hole between
> + * max(end(hole_left), iova_start).
> + *
> + * @args Arguments to allocation
> + */
> +static bool iova_tree_alloc_map_in_hole(const struct IOVATreeAllocArgs *args)
> +{
> +    const DMAMap *left = args->hole_left, *right = args->hole_right;
> +    uint64_t hole_start, hole_last;
> +
> +    if (right && right->iova + right->size < args->iova_begin) {
> +        return false;
> +    }
> +
> +    if (left && left->iova > args->iova_last) {
> +        return false;
> +    }
> +
> +    hole_start = MAX(left ? left->iova + left->size + 1 : 0, args->iova_begin);
> +    hole_last = MIN(right ? right->iova : HWADDR_MAX, args->iova_last);
> +
> +    if (hole_last - hole_start > args->new_size) {
> +        /* We found a valid hole. */
> +        return true;
> +    }
> +
> +    /* Keep iterating */
> +    return false;
> +}
> +
> +/**
> + * Foreach dma node in the tree, compare if there is a hole wit its previous
> + * node (or minimum iova address allowed) and the node.
> + *
> + * @key   Node iterating
> + * @value Node iterating
> + * @pargs Struct to communicate with the outside world
> + *
> + * Return: false to keep iterating, true if needs break.
> + */
> +static gboolean iova_tree_alloc_traverse(gpointer key, gpointer value,
> +                                         gpointer pargs)
> +{
> +    struct IOVATreeAllocArgs *args = pargs;
> +    DMAMap *node = value;
> +
> +    assert(key == value);
> +
> +    iova_tree_alloc_args_iterate(args, node);
> +    if (args->hole_left && args->hole_left->iova > args->iova_last) {
> +        return true;
> +    }
> +
> +    if (iova_tree_alloc_map_in_hole(args)) {
> +        return true;
> +    }
> +
> +    return false;
> +}
> +
> +int iova_tree_alloc(IOVATree *tree, DMAMap *map, hwaddr iova_begin,
> +                    hwaddr iova_last)
> +{
> +    struct IOVATreeAllocArgs args = {
> +        .new_size = map->size,
> +        .iova_begin = iova_begin,
> +        .iova_last = iova_last,
> +    };
> +
> +    if (iova_begin == 0) {
> +        /* Some devices does not like addr 0 */
> +        iova_begin += qemu_real_host_page_size;
> +    }
> +
> +    assert(iova_begin < iova_last);
> +
> +    /*
> +     * Find a valid hole for the mapping
> +     *
> +     * Assuming low iova_begin, so no need to do a binary search to
> +     * locate the first node.
> +     *
> +     * TODO: We can improve the search speed if we save the beginning and the
> +     * end of holes, so we don't iterate over the previous saved ones.
> +     *
> +     * TODO: Replace all this with g_tree_node_first/next/last when available
> +     * (from glib since 2.68). To do it with g_tree_foreach complicates the
> +     * code a lot.


To say the truth, the codes in iova_tree_alloc_traverse() is hard to be 
reviewed. I think it would be easy to use first/next/last. What we 
really need is to calculate the hole between two ranges with handmade 
first, last.

Thanks


> +     *
> +     */
> +    g_tree_foreach(tree->tree, iova_tree_alloc_traverse, &args);
> +    if (!iova_tree_alloc_map_in_hole(&args)) {
> +        /*
> +         * 2nd try: Last iteration left args->right as the last DMAMap. But
> +         * (right, end) hole needs to be checked too
> +         */
> +        iova_tree_alloc_args_iterate(&args, NULL);
> +        if (!iova_tree_alloc_map_in_hole(&args)) {
> +            return IOVA_ERR_NOMEM;
> +        }
> +    }
> +
> +    map->iova = MAX(iova_begin,
> +                    args.hole_left ?
> +                    args.hole_left->iova + args.hole_left->size + 1 : 0);
> +    return iova_tree_insert(tree, map);
> +}
> +
>   void iova_tree_destroy(IOVATree *tree)
>   {
>       g_tree_destroy(tree->tree);