2.6.27-stable review patch. If anyone has any objections, please let us know. ------------------ From: Ravikiran G Thirumalai commit 9e41bff2708e420e61e6b89a54c15232857069b1 upstream 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 Acked-by: H. Peter Anvin Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- arch/x86/mm/pat.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/arch/x86/mm/pat.c +++ b/arch/x86/mm/pat.c @@ -403,12 +403,16 @@ static inline int range_is_allowed(unsig 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 -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/