Re: [PATCH v2 08/14] util: Add iova_tree_alloc

[Jason Wang <jasowang@redhat.com>]

在 2022/2/27 下午9:41, 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>
> Reviewed-by: Peter Xu <peterx@redhat.com>
> ---
>   include/qemu/iova-tree.h |  18 ++++++
>   util/iova-tree.c         | 133 +++++++++++++++++++++++++++++++++++++++
>   2 files changed, 151 insertions(+)
>
> diff --git a/include/qemu/iova-tree.h b/include/qemu/iova-tree.h
> index 8249edd764..a623136cd8 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 */
>   
>   typedef struct IOVATree IOVATree;
>   typedef struct DMAMap {
> @@ -119,6 +120,23 @@ const DMAMap *iova_tree_find_address(const IOVATree *tree, hwaddr iova);
>    */
>   void iova_tree_foreach(IOVATree *tree, iova_tree_iterator iterator);
>   
> +/**
> + * iova_tree_alloc:


Should be iova_tree_alloc_map.


> + *
> + * @tree: the iova tree to allocate from
> + * @map: the new map (as translated addr & size) to allocate in the 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 return error if
> + * iova tree is out of free contiguous range. The caller gets the assigned iova
> + * in map->iova.
> + */
> +int iova_tree_alloc_map(IOVATree *tree, DMAMap *map, hwaddr iova_begin,
> +                        hwaddr iova_end);
> +
>   /**
>    * iova_tree_destroy:
>    *
> diff --git a/util/iova-tree.c b/util/iova-tree.c
> index 23ea35b7a4..302b01f1cc 100644
> --- a/util/iova-tree.c
> +++ b/util/iova-tree.c
> @@ -16,6 +16,39 @@ 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;
> +
> +    /* Map at the left of the hole, can be NULL if "this" is first one */
> +    const DMAMap *prev;
> +
> +    /* Map at the right of the hole, can be NULL if "prev" is the last one */
> +    const DMAMap *this;
> +
> +    /* If found, we fill in the IOVA here */
> +    hwaddr iova_result;
> +
> +    /* Whether have we found a valid IOVA */
> +    bool iova_found;
> +};
> +
> +/**
> + * Iterate args to the 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->prev = args->this;
> +    args->this = next;
> +}
> +
>   static int iova_tree_compare(gconstpointer a, gconstpointer b, gpointer data)
>   {
>       const DMAMap *m1 = a, *m2 = b;
> @@ -107,6 +140,106 @@ int iova_tree_remove(IOVATree *tree, const DMAMap *map)
>       return IOVA_OK;
>   }
>   
> +/**
> + * Try to find an unallocated IOVA range between prev and this elements.
> + *
> + * @args Arguments to allocation
> + *
> + * Cases:
> + *
> + * (1) !prev, !this: No entries allocated, always succeed
> + *
> + * (2) !prev, this: We're iterating at the 1st element.
> + *
> + * (3) prev, !this: We're iterating at the last element.
> + *
> + * (4) prev, this: this is the most common case, we'll try to find a hole
> + * between "prev" and "this" mapping.
> + *
> + * Note that this function assumes the last valid iova is HWADDR_MAX, but it
> + * searches linearly so it's easy to discard the result if it's not the case.
> + */
> +static void iova_tree_alloc_map_in_hole(struct IOVATreeAllocArgs *args)
> +{
> +    const DMAMap *prev = args->prev, *this = args->this;
> +    uint64_t hole_start, hole_last;
> +
> +    if (this && this->iova + this->size < args->iova_begin) {
> +        return;
> +    }
> +
> +    hole_start = MAX(prev ? prev->iova + prev->size + 1 : 0, args->iova_begin);
> +    hole_last = this ? this->iova : HWADDR_MAX;


Do we need to use iova_last instead of HWADDR_MAX?


> +
> +    if (hole_last - hole_start > args->new_size) {
> +        args->iova_result = hole_start;
> +        args->iova_found = true;
> +    }
> +}
> +
> +/**
> + * Foreach dma node in the tree, compare if there is a hole with 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);
> +    iova_tree_alloc_map_in_hole(args);
> +    return args->iova_found;
> +}
> +
> +int iova_tree_alloc_map(IOVATree *tree, DMAMap *map, hwaddr iova_begin,
> +                        hwaddr iova_last)
> +{
> +    struct IOVATreeAllocArgs args = {
> +        .new_size = map->size,
> +        .iova_begin = iova_begin,
> +    };
> +
> +    assert(iova_begin < iova_last);


Should we use "<=" here, otherwise we disallow allocate the size of 1.

And maybe we should return error instead of assert.


> +
> +    /*
> +     * 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: 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.
> +     *


One more question

The current code looks work but still a little bit complicated to be 
reviewed. Looking at the missing helpers above, if the add and remove 
are seldom. I wonder if we can simply do

g_tree_foreach() during each add/del to build a sorted list then we can 
emulate g_tree_node_first/next/last easily?


> +     */
> +    g_tree_foreach(tree->tree, iova_tree_alloc_traverse, &args);
> +    if (!args.iova_found) {
> +        /*
> +         * Either tree is empty or the last hole is still not checked.
> +         * g_tree_foreach does not compare (last, iova_end] range, so we check


"(last, iova_last]" ?

Thanks


> +         * it here.
> +         */
> +        iova_tree_alloc_args_iterate(&args, NULL);
> +        iova_tree_alloc_map_in_hole(&args);
> +    }
> +
> +    if (!args.iova_found || args.iova_result + map->size > iova_last) {
> +        return IOVA_ERR_NOMEM;
> +    }
> +
> +    map->iova = args.iova_result;
> +    return iova_tree_insert(tree, map);
> +}
> +
>   void iova_tree_destroy(IOVATree *tree)
>   {
>       g_tree_destroy(tree->tree);