On Wed, 18 Oct 2023 19:47:16 +0800 Yunsheng Lin wrote: > > mention it in the documentation. Plus the kdoc of the function should > > say that this is just a thin wrapper around other page pool APIs, and > > it's safe to mix it with other page pool APIs? > > I am not sure I understand what do 'safe' and 'mix' mean here. > > For 'safe' part, I suppose you mean if there is a va accociated with > a 'struct page' without calling some API like kmap()? For that, I suppose > it is safe when the driver is calling page_pool API without the > __GFP_HIGHMEM flag. Maybe we should mention that in the kdoc and give a > warning if page_pool_*alloc_va() is called with the __GFP_HIGHMEM flag? Sounds good. Warning wrapped in #if CONFIG_DEBUG_NET perhaps? > For the 'mix', I suppose you mean the below: > 1. Allocate a page with the page_pool_*alloc_va() API and free a page with > page_pool_free() API. > 2. Allocate a page with the page_pool_*alloc() API and free a page with > page_pool_free_va() API. > > For 1, it seems it is ok as some virt_to_head_page() and page_address() call > between va and 'struct page' does not seem to change anything if we have > enforce page_pool_*alloc_va() to be called without the __GFP_HIGHMEM flag. > > For 2, If the va is returned from page_address() which the allocation API is > called without __GFP_HIGHMEM flag. If not, the va is from kmap*()? which means > we may be calling page_pool_free_va() before kunmap*()? Is that possible? Right, if someone passes kmap()'ed address they are trying quite hard to break their own driver. Technically possible but I wouldn't worry. I just mean that in the common case of non-HIGHMEM page, calling page_pool_free_va() with the address returned by page_address() is perfectly legal.
