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net: devmem: replace gen_pool with freelist

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devmem only needs fixed-size net_iov allocations for each dma-buf binding.
The gen_pool tracks the same free set indirectly through DMA addresses,
which makes devmem depend on the generic allocator even though the users
are fixed-size net_iov chunks.

Mirror the io_uring zcrx model more closely by keeping a binding-level
freelist protected by spin_lock_bh(). Use a single net_iov_area owner for
the binding, populate each net_iov's DMA address while walking the SG
table, and check at teardown that all net_iovs have returned to the
freelist.

Validate the DMA-BUF size against the net_iov size up front and derive the
RX and TX entry count from it, avoiding a separate SG-table pass.

Drop the NET_DEVMEM select of GENERIC_ALLOCATOR now that devmem no longer
calls gen_pool APIs.

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20260917181116.3319017-2-sdf@fomichev.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Stanislav Fomichev 2026-09-17 11:11:14 -07:00 committed by Jakub Kicinski
parent cd7e4b1e47
commit 083e64a3af
3 changed files with 90 additions and 112 deletions
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1
net/Kconfig
View File

@ -68,7 +68,6 @@ config SKB_EXTENSIONS
config NET_DEVMEM
def_bool y
select GENERIC_ALLOCATOR
depends on DMA_SHARED_BUFFER
depends on PAGE_POOL

186
net/core/devmem.c
View File

@ -8,7 +8,6 @@
*/
#include <linux/dma-buf.h>
#include <linux/genalloc.h>
#include <linux/mm.h>
#include <linux/netdevice.h>
#include <linux/types.h>
@ -30,23 +29,13 @@ static DEFINE_XARRAY_FLAGS(net_devmem_dmabuf_bindings, XA_FLAGS_ALLOC1);
static const struct memory_provider_ops dmabuf_devmem_ops;
static void net_devmem_dmabuf_free_chunk_owner(struct gen_pool *genpool,
struct gen_pool_chunk *chunk,
void *not_used)
static void
net_devmem_dmabuf_free_chunk_owner(struct dmabuf_genpool_chunk_owner *owner)
{
struct dmabuf_genpool_chunk_owner *owner = chunk->owner;
kvfree(owner->area.niovs);
kfree(owner);
}
static dma_addr_t net_devmem_get_dma_addr(const struct net_iov *niov)
{
struct dmabuf_genpool_chunk_owner *owner;
owner = net_devmem_iov_to_chunk_owner(niov);
return owner->base_dma_addr +
((dma_addr_t)net_iov_idx(niov) << owner->binding->niov_shift);
if (owner) {
kvfree(owner->area.niovs);
kfree(owner);
}
}
static void net_devmem_dmabuf_binding_release(struct percpu_ref *ref)
@ -62,24 +51,20 @@ void __net_devmem_dmabuf_binding_free(struct work_struct *wq)
{
struct net_devmem_dmabuf_binding *binding = container_of(wq, typeof(*binding), unbind_w);
size_t size, avail;
gen_pool_for_each_chunk(binding->chunk_pool,
net_devmem_dmabuf_free_chunk_owner, NULL);
size = gen_pool_size(binding->chunk_pool);
avail = gen_pool_avail(binding->chunk_pool);
if (!WARN(size != avail, "can't destroy genpool. size=%zu, avail=%zu",
size, avail))
gen_pool_destroy(binding->chunk_pool);
if (binding->freelist)
WARN(binding->free_count != binding->chunk_owner->area.num_niovs,
"destroying dmabuf binding with outstanding net_iovs: total=%zu, free=%zu",
binding->chunk_owner->area.num_niovs,
binding->free_count);
net_devmem_dmabuf_free_chunk_owner(binding->chunk_owner);
dma_buf_unmap_attachment_unlocked(binding->attachment, binding->sgt,
binding->direction);
dma_buf_detach(binding->dmabuf, binding->attachment);
dma_buf_put(binding->dmabuf);
xa_destroy(&binding->bound_rxqs);
percpu_ref_exit(&binding->ref);
kvfree(binding->freelist);
kvfree(binding->tx_vec);
kfree(binding);
}
@ -87,21 +72,15 @@ void __net_devmem_dmabuf_binding_free(struct work_struct *wq)
struct net_iov *
net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding)
{
struct dmabuf_genpool_chunk_owner *owner;
unsigned long dma_addr;
struct net_iov *niov;
ssize_t offset;
ssize_t index;
dma_addr = gen_pool_alloc_owner(binding->chunk_pool,
1UL << binding->niov_shift,
(void **)&owner);
if (!dma_addr)
spin_lock_bh(&binding->freelist_lock);
if (unlikely(!binding->free_count)) {
spin_unlock_bh(&binding->freelist_lock);
return NULL;
}
offset = dma_addr - owner->base_dma_addr;
index = offset >> binding->niov_shift;
niov = &owner->area.niovs[index];
niov = binding->freelist[--binding->free_count];
spin_unlock_bh(&binding->freelist_lock);
niov->desc.pp_magic = 0;
niov->desc.pp = NULL;
@ -113,14 +92,16 @@ net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding)
void net_devmem_free_dmabuf(struct net_iov *niov)
{
struct net_devmem_dmabuf_binding *binding = net_devmem_iov_binding(niov);
unsigned long dma_addr = net_devmem_get_dma_addr(niov);
size_t niov_size = 1UL << binding->niov_shift;
if (WARN_ON(!gen_pool_has_addr(binding->chunk_pool, dma_addr,
niov_size)))
spin_lock_bh(&binding->freelist_lock);
if (WARN_ON_ONCE(binding->free_count >=
binding->chunk_owner->area.num_niovs)) {
spin_unlock_bh(&binding->freelist_lock);
return;
}
gen_pool_free(binding->chunk_pool, dma_addr, niov_size);
binding->freelist[binding->free_count++] = niov;
spin_unlock_bh(&binding->freelist_lock);
}
void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding)
@ -194,12 +175,15 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev,
struct netlink_ext_ack *extack)
{
struct net_devmem_dmabuf_binding *binding;
struct dmabuf_genpool_chunk_owner *owner;
size_t niov_size = 1UL << niov_shift;
static u32 id_alloc_next;
struct scatterlist *sg;
struct dma_buf *dmabuf;
unsigned int sg_idx, i;
unsigned long virtual;
unsigned int sg_idx;
size_t total_niovs;
size_t niov_idx;
size_t i;
int err;
if (!dma_dev) {
@ -249,33 +233,55 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev,
goto err_detach;
}
if (!IS_ALIGNED(dmabuf->size, niov_size)) {
err = -EINVAL;
NL_SET_ERR_MSG_FMT(extack,
"dmabuf size %zu not aligned to niov size %zu",
dmabuf->size, niov_size);
goto err_unmap;
}
total_niovs = dmabuf->size >> niov_shift;
if (direction == DMA_TO_DEVICE) {
if (!IS_ALIGNED(dmabuf->size, PAGE_SIZE)) {
err = -EINVAL;
NL_SET_ERR_MSG(extack, "TX dma-buf size must be a multiple of PAGE_SIZE");
goto err_unmap;
}
binding->tx_vec = kvmalloc_objs(struct net_iov *,
dmabuf->size / PAGE_SIZE);
binding->tx_vec = kvmalloc_objs(struct net_iov *, total_niovs);
if (!binding->tx_vec) {
err = -ENOMEM;
goto err_unmap;
}
} else {
spin_lock_init(&binding->freelist_lock);
binding->freelist = kvmalloc_array(total_niovs,
sizeof(binding->freelist[0]),
GFP_KERNEL);
if (!binding->freelist) {
err = -ENOMEM;
goto err_unmap;
}
}
binding->chunk_pool = gen_pool_create(niov_shift,
dev_to_node(&dev->dev));
if (!binding->chunk_pool) {
owner = kzalloc_node(sizeof(*owner), GFP_KERNEL,
dev_to_node(&dev->dev));
if (!owner) {
err = -ENOMEM;
goto err_tx_vec;
goto err_free_freelist;
}
virtual = 0;
owner->area.base_virtual = 0;
owner->area.num_niovs = total_niovs;
owner->binding = binding;
owner->area.niovs = kvmalloc_objs(*owner->area.niovs,
owner->area.num_niovs);
if (!owner->area.niovs) {
err = -ENOMEM;
goto err_free_owner;
}
binding->chunk_owner = owner;
niov_idx = 0;
for_each_sgtable_dma_sg(binding->sgt, sg, sg_idx) {
dma_addr_t dma_addr = sg_dma_address(sg);
struct dmabuf_genpool_chunk_owner *owner;
size_t len = sg_dma_len(sg);
struct net_iov *niov;
size_t nr_niovs;
if (!IS_ALIGNED(dma_addr, niov_size) ||
!IS_ALIGNED(len, niov_size)) {
@ -283,64 +289,40 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev,
NL_SET_ERR_MSG_FMT(extack,
"dmabuf sg entry (addr=%pad, len=%zu) not aligned to niov size %zu",
&dma_addr, len, niov_size);
goto err_free_chunks;
goto err_free_chunk_owner;
}
owner = kzalloc_node(sizeof(*owner), GFP_KERNEL,
dev_to_node(&dev->dev));
if (!owner) {
err = -ENOMEM;
goto err_free_chunks;
}
owner->area.base_virtual = virtual;
owner->base_dma_addr = dma_addr;
owner->area.num_niovs = len >> niov_shift;
owner->binding = binding;
err = gen_pool_add_owner(binding->chunk_pool, dma_addr,
dma_addr, len, dev_to_node(&dev->dev),
owner);
if (err) {
kfree(owner);
err = -EINVAL;
goto err_free_chunks;
}
owner->area.niovs = kvmalloc_objs(*owner->area.niovs,
owner->area.num_niovs);
if (!owner->area.niovs) {
err = -ENOMEM;
goto err_free_chunks;
}
for (i = 0; i < owner->area.num_niovs; i++) {
niov = &owner->area.niovs[i];
nr_niovs = len >> niov_shift;
for (i = 0; i < nr_niovs; i++, niov_idx++) {
niov = &owner->area.niovs[niov_idx];
net_iov_init(niov, &owner->area, NET_IOV_DMABUF);
page_pool_set_dma_addr_netmem(net_iov_to_netmem(niov),
net_devmem_get_dma_addr(niov));
dma_addr);
if (direction == DMA_TO_DEVICE)
binding->tx_vec[owner->area.base_virtual / PAGE_SIZE + i] = niov;
binding->tx_vec[niov_idx] = niov;
else
binding->freelist[binding->free_count++] = niov;
dma_addr += niov_size;
}
virtual += len;
}
err = xa_alloc_cyclic(&net_devmem_dmabuf_bindings, &binding->id,
binding, xa_limit_32b, &id_alloc_next,
GFP_KERNEL);
if (err < 0)
goto err_free_chunks;
goto err_free_chunk_owner;
list_add(&binding->list, &priv->bindings);
return binding;
err_free_chunks:
gen_pool_for_each_chunk(binding->chunk_pool,
net_devmem_dmabuf_free_chunk_owner, NULL);
gen_pool_destroy(binding->chunk_pool);
err_tx_vec:
err_free_chunk_owner:
net_devmem_dmabuf_free_chunk_owner(binding->chunk_owner);
goto err_free_freelist;
err_free_owner:
kfree(owner);
err_free_freelist:
kvfree(binding->freelist);
kvfree(binding->tx_vec);
err_unmap:
dma_buf_unmap_attachment_unlocked(binding->attachment, binding->sgt,

15
net/core/devmem.h
View File

@ -14,6 +14,7 @@
#include <net/netdev_netlink.h>
struct netlink_ext_ack;
struct dmabuf_genpool_chunk_owner;
struct net_devmem_dmabuf_binding {
struct dma_buf *dmabuf;
@ -26,7 +27,7 @@ struct net_devmem_dmabuf_binding {
* dereferenced.
*/
void *vdev;
struct gen_pool *chunk_pool;
struct dmabuf_genpool_chunk_owner *chunk_owner;
/* Protect dev */
struct mutex lock;
@ -57,6 +58,10 @@ struct net_devmem_dmabuf_binding {
/* rxq's this binding is active on. */
struct xarray bound_rxqs;
spinlock_t freelist_lock ____cacheline_aligned_in_smp;
size_t free_count;
struct net_iov **freelist;
/* ID of this binding. Globally unique to all bindings currently
* active.
*/
@ -77,17 +82,9 @@ struct net_devmem_dmabuf_binding {
};
#if defined(CONFIG_NET_DEVMEM)
/* Owner of the dma-buf chunks inserted into the gen pool. Each scatterlist
* entry from the dmabuf is inserted into the genpool as a chunk, and needs
* this owner struct to keep track of some metadata necessary to create
* allocations from this chunk.
*/
struct dmabuf_genpool_chunk_owner {
struct net_iov_area area;
struct net_devmem_dmabuf_binding *binding;
/* dma_addr of the start of the chunk. */
dma_addr_t base_dma_addr;
};
void __net_devmem_dmabuf_binding_free(struct work_struct *wq);