From a880e7623397bcb44877b012cd65baa11ad1bbf8 Mon Sep 17 00:00:00 2001 From: Roland Dreier Date: Mon, 15 Sep 2008 10:43:35 +0000 Subject: [PATCH] powerpc: Avoid integer overflow in page_is_ram() Commit 8b150478 ("ppc: make phys_mem_access_prot() work with pfns instead of addresses") fixed page_is_ram() in arch/ppc to avoid overflow for addresses above 4G on 32-bit kernels. However arch/powerpc's page_is_ram() is missing the same fix -- it computes a physical address by doing pfn << PAGE_SHIFT, which overflows if pfn corresponds to a page above 4G. In particular this causes pages above 4G to be mapped with the wrong caching attribute; for example many ppc440-based SoCs have PCI space above 4G, and mmap()ing MMIO space may end up with a mapping that has caching enabled. Fix this by working with the pfn and avoiding the conversion to physical address that causes the overflow. This patch compares the pfn to max_pfn, which is a semantic change from the old code -- that code compared the physical address to high_memory, which corresponds to max_low_pfn. However, I think that was is another bug, since highmem pages are still RAM. Reported-by: vb Signed-off-by: Roland Dreier Acked-by: Benjamin Herrenschmidt Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/mm/mem.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c index 1c93c255873b..98d7bf99533a 100644 --- a/arch/powerpc/mm/mem.c +++ b/arch/powerpc/mm/mem.c @@ -75,11 +75,10 @@ static inline pte_t *virt_to_kpte(unsigned long vaddr) int page_is_ram(unsigned long pfn) { - unsigned long paddr = (pfn << PAGE_SHIFT); - #ifndef CONFIG_PPC64 /* XXX for now */ - return paddr < __pa(high_memory); + return pfn < max_pfn; #else + unsigned long paddr = (pfn << PAGE_SHIFT); int i; for (i=0; i < lmb.memory.cnt; i++) { unsigned long base;