On Tue, Dec 12, 2023 at 06:26:51AM -0800, Mina Almasry wrote:
On Tue, Dec 12, 2023 at 4:25 AM Jason Gunthorpe jgg@nvidia.com wrote:
On Thu, Dec 07, 2023 at 04:52:39PM -0800, Mina Almasry wrote:
+static inline struct page_pool_iov *page_to_page_pool_iov(struct page *page) +{
if (page_is_page_pool_iov(page))return (struct page_pool_iov *)((unsigned long)page & ~PP_IOV);DEBUG_NET_WARN_ON_ONCE(true);return NULL;+}
We already asked not to do this, please do not allocate weird things can call them 'struct page' when they are not. It undermines the maintainability of the mm to have things mis-typed like this. Introduce a new type for your thing so the compiler can check it properly.
There is a new type introduced, it's the page_pool_iov. We set the LSB on page_pool_iov* and cast it to page* only to avoid the churn of renaming page* to page_pool_iov* in the page_pool and all the net drivers using it. Is that not a reasonable compromise in your opinion? Since the LSB is set on the resulting page pointers, they are not actually usuable as pages, and are never passed to mm APIs per your requirement.
There were two asks, the one you did was to never pass this non-struct page memory to the mm, which is great.
The other was to not mistype things, and don't type something as struct page when it is, in fact, not.
I fear what you've done is make it so only one driver calls these special functions and left the other drivers passing the struct page directly to the mm and sort of obfuscating why it is OK based on this netdev knowledge of not enabling/using the static branch in the other cases.
Perhaps you can simply avoid this by arranging for this driver to also exclusively use some special type to indicate the dual nature of the pointer and leave the other drivers as using the struct page version.
Jason