>From 9f57bd4d6dc69a4e3bf43044fa00fcd24dd363e3 Mon Sep 17 00:00:00 2001 From: Eugene Surovegin <ebs@xxxxxxxxxxx> Date: Thu, 15 Dec 2011 11:25:59 -0800 per_cpu_ptr_to_phys() incorrectly rounds up its result for non-kmalloc case to the page boundary, which is bogus for any non-page-aligned address. This affects the only in-tree user of this function - sysfs handler for per-cpu 'crash_notes' physical address. The trouble is that the crash_notes per-cpu variable is not page-aligned: crash_notes = 0xc08e8ed4 PER-CPU OFFSET VALUES: CPU 0: 3711f000 CPU 1: 37129000 CPU 2: 37133000 CPU 3: 3713d000 So, the per-cpu addresses are: crash_notes on CPU 0: f7a07ed4 => phys 36b57ed4 crash_notes on CPU 1: f7a11ed4 => phys 36b4ded4 crash_notes on CPU 2: f7a1bed4 => phys 36b43ed4 crash_notes on CPU 3: f7a25ed4 => phys 36b39ed4 However, /sys/devices/system/cpu/cpu*/crash_notes says: /sys/devices/system/cpu/cpu0/crash_notes: 36b57000 /sys/devices/system/cpu/cpu1/crash_notes: 36b4d000 /sys/devices/system/cpu/cpu2/crash_notes: 36b43000 /sys/devices/system/cpu/cpu3/crash_notes: 36b39000 As you can see, all values are rounded down to a page boundary. Consequently, this is where kexec sets up the NOTE segments, and thus where the secondary kernel is looking for them. However, when the first kernel crashes, it saves the notes to the unaligned addresses, where they are not found. Fix it by adding offset_in_page() to the translated page address. -tj: Combined Eugene's and Petr's commit messages. Signed-off-by: Eugene Surovegin <ebs@xxxxxxxxxxx> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> Reported-by: Petr Tesarik <ptesarik@xxxxxxx> Cc: stable@xxxxxxxxxx --- I combined Petr's explanation into patch description and committed it into percpu/for-3.2-fixes. Will push it to Linus in a few days. Thank you. mm/percpu.c | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/percpu.c b/mm/percpu.c index 3bb810a..716eb4a 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -1023,9 +1023,11 @@ phys_addr_t per_cpu_ptr_to_phys(void *addr) if (!is_vmalloc_addr(addr)) return __pa(addr); else - return page_to_phys(vmalloc_to_page(addr)); + return page_to_phys(vmalloc_to_page(addr)) + + offset_in_page(addr); } else - return page_to_phys(pcpu_addr_to_page(addr)); + return page_to_phys(pcpu_addr_to_page(addr)) + + offset_in_page(addr); } /** -- 1.7.3.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>