Re: [RFC v3 21/29] vhost: Add VhostIOVATree

[Jason Wang <jasowang@redhat.com>]

在 2021/5/20 上午12:28, Eugenio Pérez 写道:
> This tree is able to look for a translated address from a IOVA address.
>
> At first glance is similar to util/iova-tree. However, SVQ working on
> devices with limited IOVA space need more capabilities, like allocating
> IOVA chunks or perform reverse translations (qemu addresses to iova).
>
> Starting a sepparated implementation. Knowing than insertions/deletions
> will not be as frequent as searches,


This might not be true if vIOMMU is enabled.


> it uses an ordered array at
> implementation.


I wonder how much overhead could g_array be if it needs to grow.


>   A different name could be used, but ordered
> searchable array is a little bit long though.


Note that we had a very good example for this. That is the kernel iova 
allocator which is implemented via rbtree.

Instead of figuring out g_array vs g_tree stuffs, I would simple go with 
g_tree first (based on util/iova-tree) and borrow the well design kernel 
iova allocator API to have a generic IOVA one instead of coupling it 
with vhost. It could be used by other userspace driver in the future:

init_iova_domain()/put_iova_domain();

alloc_iova()/free_iova();

find_iova();

Another reference is the iova allocator that is implemented in VFIO.

Thanks


>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>   hw/virtio/vhost-iova-tree.h |  50 ++++++++++
>   hw/virtio/vhost-iova-tree.c | 188 ++++++++++++++++++++++++++++++++++++
>   hw/virtio/meson.build       |   2 +-
>   3 files changed, 239 insertions(+), 1 deletion(-)
>   create mode 100644 hw/virtio/vhost-iova-tree.h
>   create mode 100644 hw/virtio/vhost-iova-tree.c
>
> diff --git a/hw/virtio/vhost-iova-tree.h b/hw/virtio/vhost-iova-tree.h
> new file mode 100644
> index 0000000000..2a44af8b3a
> --- /dev/null
> +++ b/hw/virtio/vhost-iova-tree.h
> @@ -0,0 +1,50 @@
> +/*
> + * vhost software live migration ring
> + *
> + * SPDX-FileCopyrightText: Red Hat, Inc. 2021
> + * SPDX-FileContributor: Author: Eugenio Pérez <eperezma@redhat.com>
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#ifndef HW_VIRTIO_VHOST_IOVA_TREE_H
> +#define HW_VIRTIO_VHOST_IOVA_TREE_H
> +
> +#include <gmodule.h>
> +
> +#include "exec/memory.h"
> +
> +typedef struct VhostDMAMap {
> +    void *translated_addr;
> +    hwaddr iova;
> +    hwaddr size;                /* Inclusive */
> +    IOMMUAccessFlags perm;
> +} VhostDMAMap;
> +
> +typedef enum VhostDMAMapNewRC {
> +    VHOST_DMA_MAP_OVERLAP = -2,
> +    VHOST_DMA_MAP_INVALID = -1,
> +    VHOST_DMA_MAP_OK = 0,
> +} VhostDMAMapNewRC;
> +
> +/**
> + * VhostIOVATree
> + *
> + * Store and search IOVA -> Translated mappings.
> + *
> + * Note that it cannot remove nodes.
> + */
> +typedef struct VhostIOVATree {
> +    /* Ordered array of reverse translations, IOVA address to qemu memory. */
> +    GArray *iova_taddr_map;
> +} VhostIOVATree;
> +
> +void vhost_iova_tree_new(VhostIOVATree *iova_rm);
> +void vhost_iova_tree_destroy(VhostIOVATree *iova_rm);
> +
> +const VhostDMAMap *vhost_iova_tree_find_taddr(const VhostIOVATree *iova_rm,
> +                                              const VhostDMAMap *map);
> +VhostDMAMapNewRC vhost_iova_tree_insert(VhostIOVATree *iova_rm,
> +                                        VhostDMAMap *map);
> +
> +#endif
> diff --git a/hw/virtio/vhost-iova-tree.c b/hw/virtio/vhost-iova-tree.c
> new file mode 100644
> index 0000000000..dfd7e448b5
> --- /dev/null
> +++ b/hw/virtio/vhost-iova-tree.c
> @@ -0,0 +1,188 @@
> +/*
> + * vhost software live migration ring
> + *
> + * SPDX-FileCopyrightText: Red Hat, Inc. 2021
> + * SPDX-FileContributor: Author: Eugenio Pérez <eperezma@redhat.com>
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "qemu/osdep.h"
> +#include "vhost-iova-tree.h"
> +
> +#define G_ARRAY_NOT_ZERO_TERMINATED false
> +#define G_ARRAY_NOT_CLEAR_ON_ALLOC false
> +
> +/**
> + * Inserts an element after an existing one in garray.
> + *
> + * @array      The array
> + * @prev_elem  The previous element of array of NULL if prepending
> + * @map        The DMA map
> + *
> + * It provides the aditional advantage of being type safe over
> + * g_array_insert_val, which accepts a reference pointer instead of a value
> + * with no complains.
> + */
> +static void vhost_iova_tree_insert_after(GArray *array,
> +                                         const VhostDMAMap *prev_elem,
> +                                         const VhostDMAMap *map)
> +{
> +    size_t pos;
> +
> +    if (!prev_elem) {
> +        pos = 0;
> +    } else {
> +        pos = prev_elem - &g_array_index(array, typeof(*prev_elem), 0) + 1;
> +    }
> +
> +    g_array_insert_val(array, pos, *map);
> +}
> +
> +static gint vhost_iova_tree_cmp_iova(gconstpointer a, gconstpointer b)
> +{
> +    const VhostDMAMap *m1 = a, *m2 = b;
> +
> +    if (m1->iova > m2->iova + m2->size) {
> +        return 1;
> +    }
> +
> +    if (m1->iova + m1->size < m2->iova) {
> +        return -1;
> +    }
> +
> +    /* Overlapped */
> +    return 0;
> +}
> +
> +/**
> + * Find the previous node to a given iova
> + *
> + * @array  The ascending ordered-by-translated-addr array of VhostDMAMap
> + * @map    The map to insert
> + * @prev   Returned location of the previous map
> + *
> + * Return VHOST_DMA_MAP_OK if everything went well, or VHOST_DMA_MAP_OVERLAP if
> + * it already exists. It is ok to use this function to check if a given range
> + * exists, but it will use a linear search.
> + *
> + * TODO: We can use bsearch to locate the entry if we save the state in the
> + * needle, knowing that the needle is always the first argument to
> + * compare_func.
> + */
> +static VhostDMAMapNewRC vhost_iova_tree_find_prev(const GArray *array,
> +                                                  GCompareFunc compare_func,
> +                                                  const VhostDMAMap *map,
> +                                                  const VhostDMAMap **prev)
> +{
> +    size_t i;
> +    int r;
> +
> +    *prev = NULL;
> +    for (i = 0; i < array->len; ++i) {
> +        r = compare_func(map, &g_array_index(array, typeof(*map), i));
> +        if (r == 0) {
> +            return VHOST_DMA_MAP_OVERLAP;
> +        }
> +        if (r < 0) {
> +            return VHOST_DMA_MAP_OK;
> +        }
> +
> +        *prev = &g_array_index(array, typeof(**prev), i);
> +    }
> +
> +    return VHOST_DMA_MAP_OK;
> +}
> +
> +/**
> + * Create a new IOVA tree
> + *
> + * @tree  The IOVA tree
> + */
> +void vhost_iova_tree_new(VhostIOVATree *tree)
> +{
> +    assert(tree);
> +
> +    tree->iova_taddr_map = g_array_new(G_ARRAY_NOT_ZERO_TERMINATED,
> +                                       G_ARRAY_NOT_CLEAR_ON_ALLOC,
> +                                       sizeof(VhostDMAMap));
> +}
> +
> +/**
> + * Destroy an IOVA tree
> + *
> + * @tree  The iova tree
> + */
> +void vhost_iova_tree_destroy(VhostIOVATree *tree)
> +{
> +    g_array_unref(g_steal_pointer(&tree->iova_taddr_map));
> +}
> +
> +/**
> + * Perform a search on a GArray.
> + *
> + * @array Glib array
> + * @map Map to look up
> + * @compare_func Compare function to use
> + *
> + * Return The found element or NULL if not found.
> + *
> + * This can be replaced with g_array_binary_search (Since glib 2.62) when that
> + * is common enough.
> + */
> +static const VhostDMAMap *vhost_iova_tree_bsearch(const GArray *array,
> +                                                  const VhostDMAMap *map,
> +                                                  GCompareFunc compare_func)
> +{
> +    return bsearch(map, array->data, array->len, sizeof(*map), compare_func);
> +}
> +
> +/**
> + * Find the translated address stored from a IOVA address
> + *
> + * @tree  The iova tree
> + * @map   The map with the memory address
> + *
> + * Return the stored mapping, or NULL if not found.
> + */
> +const VhostDMAMap *vhost_iova_tree_find_taddr(const VhostIOVATree *tree,
> +                                              const VhostDMAMap *map)
> +{
> +    return vhost_iova_tree_bsearch(tree->iova_taddr_map, map,
> +                                  vhost_iova_tree_cmp_iova);
> +}
> +
> +/**
> + * Insert a new map
> + *
> + * @tree  The iova tree
> + * @map   The iova map
> + *
> + * Returns:
> + * - VHOST_DMA_MAP_OK if the map fits in the container
> + * - VHOST_DMA_MAP_INVALID if the map does not make sense (like size overflow)
> + * - VHOST_DMA_MAP_OVERLAP if the tree already contains that map
> + * Can query the assignated iova in map.
> + */
> +VhostDMAMapNewRC vhost_iova_tree_insert(VhostIOVATree *tree,
> +                                        VhostDMAMap *map)
> +{
> +    const VhostDMAMap *prev;
> +    int find_prev_rc;
> +
> +    if (map->translated_addr + map->size < map->translated_addr ||
> +        map->iova + map->size < map->iova || map->perm == IOMMU_NONE) {
> +        return VHOST_DMA_MAP_INVALID;
> +    }
> +
> +    /* Check for duplicates, and save position for insertion */
> +    find_prev_rc = vhost_iova_tree_find_prev(tree->iova_taddr_map,
> +                                             vhost_iova_tree_cmp_iova, map,
> +                                             &prev);
> +    if (find_prev_rc == VHOST_DMA_MAP_OVERLAP) {
> +        return VHOST_DMA_MAP_OVERLAP;
> +    }
> +
> +    vhost_iova_tree_insert_after(tree->iova_taddr_map, prev, map);
> +    return VHOST_DMA_MAP_OK;
> +}
> diff --git a/hw/virtio/meson.build b/hw/virtio/meson.build
> index 8b5a0225fe..cb306b83c6 100644
> --- a/hw/virtio/meson.build
> +++ b/hw/virtio/meson.build
> @@ -11,7 +11,7 @@ softmmu_ss.add(when: 'CONFIG_ALL', if_true: files('vhost-stub.c'))
>   
>   virtio_ss = ss.source_set()
>   virtio_ss.add(files('virtio.c'))
> -virtio_ss.add(when: 'CONFIG_VHOST', if_true: files('vhost.c', 'vhost-backend.c', 'vhost-shadow-virtqueue.c'))
> +virtio_ss.add(when: 'CONFIG_VHOST', if_true: files('vhost.c', 'vhost-backend.c', 'vhost-shadow-virtqueue.c', 'vhost-iova-tree.c'))
>   virtio_ss.add(when: 'CONFIG_VHOST_USER', if_true: files('vhost-user.c'))
>   virtio_ss.add(when: 'CONFIG_VHOST_VDPA', if_true: files('vhost-vdpa.c'))
>   virtio_ss.add(when: 'CONFIG_VIRTIO_BALLOON', if_true: files('virtio-balloon.c'))