kernel/linux.git/net/core/devmem.c, branch v7.0-rc7

net: devmem: use READ_ONCE/WRITE_ONCE on binding->dev

2026-03-05T01:59:27+00:00

binding->dev is protected on the write-side in mp_dmabuf_devmem_uninstall() against concurrent writes, but due to the concurrent bare reads in net_devmem_get_binding() and validate_xmit_unreadable_skb() it should be wrapped in a READ_ONCE/WRITE_ONCE pair to make sure no compiler optimizations play with the underlying register in unforeseen ways. Doesn't present a critical bug because the known compiler optimizations don't result in bad behavior. There is no tearing on u64, and load omissions/invented loads would only break if additional binding->dev references were inlined together (they aren't right now). This just more strictly follows the linux memory model (i.e., "Lock-Protected Writes With Lockless Reads" in tools/memory-model/Documentation/access-marking.txt). Fixes: bd61848900bf ("net: devmem: Implement TX path") Signed-off-by: Bobby Eshleman Link: https://patch.msgid.link/20260302-devmem-membar-fix-v2-1-5b33c9cbc28b@meta.com Signed-off-by: Jakub Kicinski

Convert remaining multi-line kmalloc_obj/flex GFP_KERNEL uses

2026-02-22T16:26:33+00:00

Conversion performed via this Coccinelle script: // SPDX-License-Identifier: GPL-2.0-only // Options: --include-headers-for-types --all-includes --include-headers --keep-comments virtual patch @gfp depends on patch && !(file in "tools") && !(file in "samples")@ identifier ALLOC = {kmalloc_obj,kmalloc_objs,kmalloc_flex, kzalloc_obj,kzalloc_objs,kzalloc_flex, kvmalloc_obj,kvmalloc_objs,kvmalloc_flex, kvzalloc_obj,kvzalloc_objs,kvzalloc_flex}; @@ ALLOC(... - , GFP_KERNEL ) $ make coccicheck MODE=patch COCCI=gfp.cocci Build and boot tested x86_64 with Fedora 42's GCC and Clang: Linux version 6.19.0+ (user@host) (gcc (GCC) 15.2.1 20260123 (Red Hat 15.2.1-7), GNU ld version 2.44-12.fc42) #1 SMP PREEMPT_DYNAMIC 1970-01-01 Linux version 6.19.0+ (user@host) (clang version 20.1.8 (Fedora 20.1.8-4.fc42), LLD 20.1.8) #1 SMP PREEMPT_DYNAMIC 1970-01-01 Signed-off-by: Kees Cook Signed-off-by: Linus Torvalds

treewide: Replace kmalloc with kmalloc_obj for non-scalar types

2026-02-21T09:02:28+00:00

This is the result of running the Coccinelle script from scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to avoid scalar types (which need careful case-by-case checking), and instead replace kmalloc-family calls that allocate struct or union object instances: Single allocations: kmalloc(sizeof(TYPE), ...) are replaced with: kmalloc_obj(TYPE, ...) Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...) are replaced with: kmalloc_objs(TYPE, COUNT, ...) Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...) are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...) (where TYPE may also be *VAR) The resulting allocations no longer return "void *", instead returning "TYPE *". Signed-off-by: Kees Cook

net: inline net_is_devmem_iov()

2026-01-25T21:18:53+00:00

1) Inline this small helper to reduce code size and decrease cpu costs. 2) Constify its argument. 3) Move it to include/net/netmem.h, as a prereq for the following patch. $ scripts/bloat-o-meter -t vmlinux.2 vmlinux.3 add/remove: 0/2 grow/shrink: 0/4 up/down: 0/-158 (-158) Function old new delta validate_xmit_skb 866 857 -9 __pfx_net_is_devmem_iov 16 - -16 net_is_devmem_iov 22 - -22 get_netmem 152 130 -22 put_netmem 140 114 -26 tcp_recvmsg_locked 3860 3797 -63 Total: Before=22566015, After=22565857, chg -0.00% Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260122045720.1221017-4-edumazet@google.com Signed-off-by: Jakub Kicinski

net: devmem: convert binding refcount to percpu_ref

2026-01-13T02:00:12+00:00

Convert net_devmem_dmabuf_binding refcount from refcount_t to percpu_ref to optimize common-case reference counting on the hot path. The typical devmem workflow involves binding a dmabuf to a queue (acquiring the initial reference on binding->ref), followed by high-volume traffic where every skb fragment acquires a reference. Eventually traffic stops and the unbind operation releases the initial reference. Additionally, the high traffic hot path is often multi-core. This access pattern is ideal for percpu_ref as the first and last reference during bind/unbind normally book-ends activity in the hot path. __net_devmem_dmabuf_binding_free becomes the percpu_ref callback invoked when the last reference is dropped. kperf test: - 4MB message sizes - 60s of workload each run - 5 runs - 4 flows Throughput: Before: 45.31 GB/s (+/- 3.17 GB/s) After: 48.67 GB/s (+/- 0.01 GB/s) Picking throughput-matched kperf runs (both before and after matched at ~48 GB/s) for apples-to-apples comparison: Summary (averaged across 4 workers): TX worker CPU idle %: Before: 34.44% After: 87.13% RX worker CPU idle %: Before: 5.38% After: 9.73% kperf before: client: == Source client: Tx 98.100 Gbps (735764807680 bytes in 60001149 usec) client: Tx102.798 Gbps (770996961280 bytes in 60001149 usec) client: Tx101.534 Gbps (761517834240 bytes in 60001149 usec) client: Tx 82.794 Gbps (620966707200 bytes in 60001149 usec) client: net CPU 56: usr: 0.01% sys: 0.12% idle:17.06% iow: 0.00% irq: 9.89% sirq:72.91% client: app CPU 60: usr: 0.08% sys:63.30% idle:36.24% iow: 0.00% irq: 0.30% sirq: 0.06% client: net CPU 57: usr: 0.03% sys: 0.08% idle:75.68% iow: 0.00% irq: 2.96% sirq:21.23% client: app CPU 61: usr: 0.06% sys:67.67% idle:31.94% iow: 0.00% irq: 0.28% sirq: 0.03% client: net CPU 58: usr: 0.01% sys: 0.06% idle:76.87% iow: 0.00% irq: 2.84% sirq:20.19% client: app CPU 62: usr: 0.06% sys:69.78% idle:29.79% iow: 0.00% irq: 0.30% sirq: 0.05% client: net CPU 59: usr: 0.06% sys: 0.16% idle:74.97% iow: 0.00% irq: 3.76% sirq:21.03% client: app CPU 63: usr: 0.06% sys:59.82% idle:39.80% iow: 0.00% irq: 0.25% sirq: 0.05% client: == Target client: Rx 98.092 Gbps (735764807680 bytes in 60006084 usec) client: Rx102.785 Gbps (770962161664 bytes in 60006084 usec) client: Rx101.523 Gbps (761499566080 bytes in 60006084 usec) client: Rx 82.783 Gbps (620933136384 bytes in 60006084 usec) client: net CPU 2: usr: 0.00% sys: 0.01% idle:24.51% iow: 0.00% irq: 1.67% sirq:73.79% client: app CPU 6: usr: 1.51% sys:96.43% idle: 1.13% iow: 0.00% irq: 0.36% sirq: 0.55% client: net CPU 1: usr: 0.00% sys: 0.01% idle:25.18% iow: 0.00% irq: 1.99% sirq:72.80% client: app CPU 5: usr: 2.21% sys:94.54% idle: 2.54% iow: 0.00% irq: 0.38% sirq: 0.30% client: net CPU 3: usr: 0.00% sys: 0.01% idle:26.34% iow: 0.00% irq: 2.12% sirq:71.51% client: app CPU 7: usr: 2.22% sys:94.28% idle: 2.52% iow: 0.00% irq: 0.59% sirq: 0.37% client: net CPU 0: usr: 0.00% sys: 0.03% idle: 0.00% iow: 0.00% irq:10.44% sirq:89.51% client: app CPU 4: usr: 2.39% sys:81.46% idle:15.33% iow: 0.00% irq: 0.50% sirq: 0.30% kperf after: client: == Source client: Tx 99.257 Gbps (744447016960 bytes in 60001303 usec) client: Tx101.013 Gbps (757617131520 bytes in 60001303 usec) client: Tx 88.179 Gbps (661357854720 bytes in 60001303 usec) client: Tx101.002 Gbps (757533245440 bytes in 60001303 usec) client: net CPU 56: usr: 0.00% sys: 0.01% idle: 6.22% iow: 0.00% irq: 8.68% sirq:85.06% client: app CPU 60: usr: 0.08% sys:12.56% idle:87.21% iow: 0.00% irq: 0.08% sirq: 0.05% client: net CPU 57: usr: 0.00% sys: 0.05% idle:69.53% iow: 0.00% irq: 2.02% sirq:28.38% client: app CPU 61: usr: 0.11% sys:13.40% idle:86.36% iow: 0.00% irq: 0.08% sirq: 0.03% client: net CPU 58: usr: 0.00% sys: 0.03% idle:70.04% iow: 0.00% irq: 3.38% sirq:26.53% client: app CPU 62: usr: 0.10% sys:11.46% idle:88.31% iow: 0.00% irq: 0.08% sirq: 0.03% client: net CPU 59: usr: 0.01% sys: 0.06% idle:71.18% iow: 0.00% irq: 1.97% sirq:26.75% client: app CPU 63: usr: 0.10% sys:13.10% idle:86.64% iow: 0.00% irq: 0.10% sirq: 0.05% client: == Target client: Rx 99.250 Gbps (744415182848 bytes in 60003297 usec) client: Rx101.006 Gbps (757589737472 bytes in 60003297 usec) client: Rx 88.171 Gbps (661319475200 bytes in 60003297 usec) client: Rx100.996 Gbps (757514792960 bytes in 60003297 usec) client: net CPU 2: usr: 0.00% sys: 0.01% idle:28.02% iow: 0.00% irq: 1.95% sirq:70.00% client: app CPU 6: usr: 2.03% sys:87.20% idle:10.04% iow: 0.00% irq: 0.37% sirq: 0.33% client: net CPU 3: usr: 0.00% sys: 0.00% idle:27.63% iow: 0.00% irq: 1.90% sirq:70.45% client: app CPU 7: usr: 1.78% sys:89.70% idle: 7.79% iow: 0.00% irq: 0.37% sirq: 0.34% client: net CPU 0: usr: 0.00% sys: 0.01% idle: 0.00% iow: 0.00% irq: 9.96% sirq:90.01% client: app CPU 4: usr: 2.33% sys:83.51% idle:13.24% iow: 0.00% irq: 0.64% sirq: 0.26% client: net CPU 1: usr: 0.00% sys: 0.01% idle:27.60% iow: 0.00% irq: 1.94% sirq:70.43% client: app CPU 5: usr: 1.88% sys:89.61% idle: 7.86% iow: 0.00% irq: 0.35% sirq: 0.27% Signed-off-by: Bobby Eshleman Acked-by: Stanislav Fomichev Link: https://patch.msgid.link/20260107-upstream-precpu-ref-v2-v2-1-a709f098b3dc@meta.com Signed-off-by: Jakub Kicinski

netmem, devmem, tcp: access pp fields through @desc in net_iov

2025-11-28T01:41:51+00:00

Convert all the legacy code directly accessing the pp fields in net_iov to access them through @desc in net_iov. Signed-off-by: Byungchul Park Signed-off-by: Jakub Kicinski

net: devmem: refresh devmem TX dst in case of route invalidation

2025-10-30T02:23:21+00:00

The zero-copy Device Memory (Devmem) transmit path relies on the socket's route cache (`dst_entry`) to validate that the packet is being sent via the network device to which the DMA buffer was bound. However, this check incorrectly fails and returns `-ENODEV` if the socket's route cache entry (`dst`) is merely missing or expired (`dst == NULL`). This scenario is observed during network events, such as when flow steering rules are deleted, leading to a temporary route cache invalidation. This patch fixes -ENODEV error for `net_devmem_get_binding()` by doing the following: 1. It attempts to rebuild the route via `rebuild_header()` if the route is initially missing (`dst == NULL`). This allows the TCP/IP stack to recover from transient route cache misses. 2. It uses `rcu_read_lock()` and `dst_dev_rcu()` to safely access the network device pointer (`dst_dev`) from the route, preventing use-after-free conditions if the device is concurrently removed. 3. It maintains the critical safety check by validating that the retrieved destination device (`dst_dev`) is exactly the device registered in the Devmem binding (`binding->dev`). These changes prevent unnecessary ENODEV failures while maintaining the critical safety requirement that the Devmem resources are only used on the bound network device. Reviewed-by: Bobby Eshleman Reported-by: Eric Dumazet Reported-by: Vedant Mathur Suggested-by: Eric Dumazet Fixes: bd61848900bf ("net: devmem: Implement TX path") Signed-off-by: Shivaji Kant Link: https://patch.msgid.link/20251029065420.3489943-1-shivajikant@google.com Signed-off-by: Jakub Kicinski

net: devmem: pull out dma_dev out of net_devmem_bind_dmabuf

2025-08-28T23:05:32+00:00

Fetch the DMA device before calling net_devmem_bind_dmabuf() and pass it on as a parameter. This is needed for an upcoming change which will read the DMA device per queue. This patch has no functional changes. Signed-off-by: Dragos Tatulea Reviewed-by: Mina Almasry Link: https://patch.msgid.link/20250827144017.1529208-7-dtatulea@nvidia.com Signed-off-by: Jakub Kicinski

net: devmem: get netdev DMA device via new API

2025-08-28T23:05:31+00:00

Switch to the new API for fetching DMA devices for a netdev. The API is called with queue index 0 for now which is equivalent with the previous behavior. This patch will allow devmem to work with devices where the DMA device is not stored in the parent device. mlx5 SFs are an example of such a device. Multi-PF netdevs are still problematic (as they were before this change). Upcoming patches will address this for the rx binding. Signed-off-by: Dragos Tatulea Reviewed-by: Mina Almasry Link: https://patch.msgid.link/20250827144017.1529208-5-dtatulea@nvidia.com Signed-off-by: Jakub Kicinski

net: devmem: fix DMA direction on unmapping

2025-08-05T00:15:38+00:00

Looks like we always unmap the DMA_BUF with DMA_FROM_DEVICE direction. While at it unexport __net_devmem_dmabuf_binding_free(), it's internal. Found by code inspection. Fixes: bd61848900bf ("net: devmem: Implement TX path") Acked-by: Stanislav Fomichev Reviewed-by: Mina Almasry Link: https://patch.msgid.link/20250801011335.2267515-1-kuba@kernel.org Signed-off-by: Jakub Kicinski