From 9e41bff2708e420e61e6b89a54c15232857069b1 Mon Sep 17 00:00:00 2001 From: Ravikiran G Thirumalai Date: Thu, 30 Oct 2008 13:59:21 -0700 Subject: [PATCH] x86: fix /dev/mem mmap breakage when PAT is disabled Impact: allow /dev/mem mmaps on non-PAT CPUs/platforms Fix mmap to /dev/mem when CONFIG_X86_PAT is off and CONFIG_STRICT_DEVMEM is off mmap to /dev/mem on kernel memory has been failing since the introduction of PAT (CONFIG_STRICT_DEVMEM=n case). Seems like the check to avoid cache aliasing with PAT is kicking in even when PAT is disabled. The bug seems to have crept in 2.6.26. This patch makes sure that the mmap to regular kernel memory succeeds if CONFIG_STRICT_DEVMEM=n and PAT is disabled, and the checks to avoid cache aliasing still happens if PAT is enabled. Signed-off-by: Ravikiran Thirumalai Tested-by: Tim Sirianni Cc: Acked-by: H. Peter Anvin Signed-off-by: Ingo Molnar --- arch/x86/mm/pat.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c index 738fd0f24958..eb1bf000d12e 100644 --- a/arch/x86/mm/pat.c +++ b/arch/x86/mm/pat.c @@ -481,12 +481,16 @@ static inline int range_is_allowed(unsigned long pfn, unsigned long size) return 1; } #else +/* This check is needed to avoid cache aliasing when PAT is enabled */ static inline int range_is_allowed(unsigned long pfn, unsigned long size) { u64 from = ((u64)pfn) << PAGE_SHIFT; u64 to = from + size; u64 cursor = from; + if (!pat_enabled) + return 1; + while (cursor < to) { if (!devmem_is_allowed(pfn)) { printk(KERN_INFO -- 2.20.1