On Fri, Nov 10, 2023 at 3:16 PM Jakub Kicinski kuba@kernel.org wrote:
On Sun, 5 Nov 2023 18:44:05 -0800 Mina Almasry wrote:
+static int mp_dmabuf_devmem_init(struct page_pool *pool) +{
struct netdev_dmabuf_binding *binding = pool->mp_priv;if (!binding)return -EINVAL;if (pool->p.flags & PP_FLAG_DMA_MAP ||pool->p.flags & PP_FLAG_DMA_SYNC_DEV)return -EOPNOTSUPP;This looks backwards, we should _force_ the driver to use the dma mapping built into the page pool APIs, to isolate the driver from how the DMA addr actually gets obtained. Right?
Maybe seeing driver patches would illuminate.
The full tree with driver patches is here:
https://github.com/torvalds/linux/compare/master...mina:linux:tcpdevmem-v3
This is probably the most relevant patch, it implements POC page-pool support into GVE + devmem support:
https://github.com/torvalds/linux/commit/3c27aa21eb3374f2f1677ece6258f046da2...
But, to answer your question, yes, this is a mistake. devmem doesn't need to be mapped, which is why I disabled the flag. Actually what should happen is like you said, we should enforce that PP_FLAG_DMA_MAP is on, and have it be a no-op, so the driver doesn't try to map the devmem on its own.