From: Dave Hansen Date: Fri, 18 Nov 2022 15:16:16 +0000 (-0800) Subject: x86/mm: Ensure forced page table splitting X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=3e844d842d49cdbe61a4b338bdd512654179488a;p=linux.git x86/mm: Ensure forced page table splitting There are a few kernel users like kfence that require 4k pages to work correctly and do not support large mappings. They use set_memory_4k() to break down those large mappings. That, in turn relies on cpa_data->force_split option to indicate to set_memory code that it should split page tables regardless of whether the need to be. But, a recent change added an optimization which would return early if a set_memory request came in that did not change permissions. It did not consult ->force_split and would mistakenly optimize away the splitting that set_memory_4k() needs. This broke kfence. Skip the same-permission optimization when ->force_split is set. Fixes: 127960a05548 ("x86/mm: Inhibit _PAGE_NX changes from cpa_process_alias()") Signed-off-by: Dave Hansen Tested-by: Marco Elver Cc: Peter Zijlstra (Intel) Link: https://lore.kernel.org/all/CA+G9fYuFxZTxkeS35VTZMXwQvohu73W3xbZ5NtjebsVvH6hCuA@mail.gmail.com/ --- diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index 220361ceb9977..0db69514fe291 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -1727,7 +1727,8 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int primary) /* * No changes, easy! */ - if (!(pgprot_val(cpa->mask_set) | pgprot_val(cpa->mask_clr))) + if (!(pgprot_val(cpa->mask_set) | pgprot_val(cpa->mask_clr)) && + !cpa->force_split) return ret; while (rempages) {