Hi, On Fri, Nov 24, 2023 at 08:36:52PM +0100, David Hildenbrand wrote: > On 19.11.23 17:57, Alexandru Elisei wrote: > > Add arch_free_pages_prepare() hook that is called before that page flags > > are cleared. This will be used by arm64 when explicit management of tag > > storage pages is enabled. > > Can you elaborate a bit what exactly will be done by that code with that > information? Of course. The MTE code that is in the kernel today uses the PG_arch_2 page flag, which it renames to PG_mte_tagged, to track if a page has been mapped with tagging enabled. That flag is cleared by free_pages_prepare() when it does: page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; When tag storage management is enabled, tag storage is reserved for a page if and only if the page is mapped as tagged. When a page is freed, the code looks at the PG_mte_tagged flag to determine if the page was mapped as tagged, and therefore has tag storage reserved, to determine if the corresponding tag storage should also be freed. I have considered using arch_free_page(), but free_pages_prepare() calls the function after the flags are cleared. Does that answer your question? Alex > > -- > Cheers, > > David / dhildenb >
