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authorIngo Molnar <mingo@elte.hu>2009-02-20 17:44:21 +0100
committerIngo Molnar <mingo@elte.hu>2009-02-20 17:48:49 +0100
commit7a5714e0186030676d79a7b4b9830c8e45c3b0a1 (patch)
tree7d76720d333893db5b5fa4bb492d69a823ba76db
parent609162850db11dfe3b23f43b36888aa8b3ad7685 (diff)
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 <torvalds@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--arch/x86/mm/pageattr.c7
1 files changed, 7 insertions, 0 deletions
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) {