On 2023/11/8 6:10, Mina Almasry wrote:
On Mon, Nov 6, 2023 at 3:44 PM David Ahern dsahern@kernel.org wrote:
On 11/5/23 7:44 PM, Mina Almasry wrote:
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index eeeda849115c..1c351c138a5b 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -843,6 +843,9 @@ struct netdev_dmabuf_binding { };
#ifdef CONFIG_DMA_SHARED_BUFFER +struct page_pool_iov * +netdev_alloc_devmem(struct netdev_dmabuf_binding *binding); +void netdev_free_devmem(struct page_pool_iov *ppiov);
netdev_{alloc,free}_dmabuf?
Can do.
I say that because a dmabuf can be host memory, at least I am not aware of a restriction that a dmabuf is device memory.
In my limited experience dma-buf is generally device memory, and that's really its use case. CONFIG_UDMABUF is a driver that mocks dma-buf with a memfd which I think is used for testing. But I can do the rename, it's more clear anyway, I think.
On Mon, Nov 6, 2023 at 11:45 PM Yunsheng Lin linyunsheng@huawei.com wrote:
On 2023/11/6 10:44, Mina Almasry wrote:
+void netdev_free_devmem(struct page_pool_iov *ppiov) +{
struct netdev_dmabuf_binding *binding = page_pool_iov_binding(ppiov);refcount_set(&ppiov->refcount, 1);if (gen_pool_has_addr(binding->chunk_pool,page_pool_iov_dma_addr(ppiov), PAGE_SIZE))When gen_pool_has_addr() returns false, does it mean something has gone really wrong here?
Yes, good eye. gen_pool_has_addr() should never return false, but then again, gen_pool_free() BUG_ON()s if it doesn't find the address, which is an extremely severe reaction to what can be a minor bug in the accounting. I prefer to leak rather than crash the machine. It's a bit of defensive programming that is normally frowned upon, but I feel like in this case it's maybe warranted due to the very severe reaction (BUG_ON).
I would argue that why is the above defensive programming not done in the gen_pool core:)