From: Ingo Molnar Date: Fri, 20 Feb 2009 16:44:21 +0000 (+0100) Subject: x86, pat: add large-PAT check to split_large_page() X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=7a5714e0186030676d79a7b4b9830c8e45c3b0a1;p=linux-beck.git x86, pat: add large-PAT check to split_large_page() Impact: future-proof the split_large_page() function Linus noticed that split_large_page() is not safe wrt. the PAT bit: it is bit 12 on the 1GB and 2MB page table level (_PAGE_BIT_PAT_LARGE), and it is bit 7 on the 4K page table level (_PAGE_BIT_PAT). Currently it is not a problem because we never set _PAGE_BIT_PAT_LARGE on any of the large-page mappings - but should this happen in the future the split_large_page() would silently lift bit 12 into the lowlevel 4K pte and would start corrupting the physical page frame offset. Not fun. So add a debug warning, to make sure if something ever sets the PAT bit then this function gets updated too. Cc: Linus Torvalds Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index 7be47d1a97e4..8253bc97587e 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -482,6 +482,13 @@ static int split_large_page(pte_t *kpte, unsigned long address) pbase = (pte_t *)page_address(base); paravirt_alloc_pte(&init_mm, page_to_pfn(base)); ref_prot = pte_pgprot(pte_clrhuge(*kpte)); + /* + * If we ever want to utilize the PAT bit, we need to + * update this function to make sure it's converted from + * bit 12 to bit 7 when we cross from the 2MB level to + * the 4K level: + */ + WARN_ON_ONCE(pgprot_val(ref_prot) & _PAGE_PAT_LARGE); #ifdef CONFIG_X86_64 if (level == PG_LEVEL_1G) {