On Fri, Oct 29, 2021 at 08:35:22PM +0200, Eugenio Pérez wrote:
> 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@xxxxxxxxxx>
> ---
> 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 */
>
> 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_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;
I slightly prefer having two more fields to cache the result:
/* If found, we fill in the IOVA here */
hwaddr iova_result;
/* Whether have we found a valid IOVA */
bool iova_found;
IMHO they'll help on readability. More below.
> +};
> +
> +/**
> + * 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).
I think this functions need the most comments, and above sentence is more or
less not sounding correct... My try...
/*
* Try to find an unallocated IOVA range between LEFT and RIGHT elements.
*
* There're three cases:
*
* (1) When LEFT==NULL, RIGHT must be non-NULL and it means we're iterating at
* the 1st element.
*
* (2) When RIGHT==NULL, LEFT must be non-NULL and it means we're iterating at
* the last element.
*
* (3) When both LEFT and RIGHT are non-NULL, this is the most common case,
* we'll try to find a hole between LEFT and RIGHT mapping.
*/
> + *
> + * @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);
I assume these values should be always inclusive, hence
s/right->iova/right->iova + 1/
?
> +
> + if (hole_last - hole_start > args->new_size) {
> + /* We found a valid hole. */
IMHO it's cleaner we simply set:
args->iova_result = hole_start;
Here before stop the iterations.
> + 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) {
IMHO this check is redundant and can be dropped, as it's already done in
iova_tree_alloc_map_in_hole().
> + 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;
> + }
(This should be dropped as the new version goes)
> +
> + 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.
We could also mention something like this here:
*
* The traversing will cover all the possible holes but except the last
* hole starting from the last element. We need to handle it separately
* below.
*
> + *
> + * 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.
> + *
> + */
> + g_tree_foreach(tree->tree, iova_tree_alloc_traverse, &args);
> + if (!iova_tree_alloc_map_in_hole(&args)) {
With iova_found, here it could be (hopefully) more readable:
if (!args->iova_found) {
/* If we failed to find a hole in 0..N-1 entries, try the last one */
iova_tree_alloc_args_iterate(&args, NULL);
iova_tree_alloc_map_in_hole(&args);
if (!args->iova_found) {
return IOVA_ERR_NOMEM;
}
}
map->iova = args->iova_result;
...
Thanks,
> + /*
> + * 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);
> --
> 2.27.0
>
--
Peter Xu
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