From: Roger Pau Monne Date: Mon, 26 Nov 2018 17:55:48 +0000 (+0100) Subject: mm: make opt_bootscrub non-init X-Git-Tag: archive/raspbian/4.14.0+80-gd101b417b7-1+rpi1^2~63^2~2824 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=43fa95ae6a;p=xen.git mm: make opt_bootscrub non-init LLVM code generation can attempt to load from a variable in the next condition of an expression under certain circumstances, thus turning the following condition: if ( system_state < SYS_STATE_active && opt_bootscrub == BOOTSCRUB_IDLE ) Into: 0xffff82d080223967 <+103>: cmpl $0x3,0x37b032(%rip) # 0xffff82d08059e9a0 0xffff82d08022396e <+110>: setb -0x29(%rbp) 0xffff82d080223972 <+114>: cmpl $0x2,0x228a8b(%rip) # 0xffff82d08044c404 Such code will trigger a page fault if system_state >= SYS_STATE_active because opt_bootscrub will be unmapped. Fix this by making opt_bootscrub non-init, thus preventing the page fault. The LLVM bug with the discussion about this issue can be found at: https://bugs.llvm.org/show_bug.cgi?id=39707 I haven't been able to find any other instances of such conditional expression that uses system_state together with an init variable or function. Signed-off-by: Roger Pau Monné Reviewed-by: Sergey Dyasli Acked-by: Andrew Cooper Acked-by: Julien Grall Acked-by: Wei Liu --- diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c index 4a2cbda1db..fd3b0aaa83 100644 --- a/xen/common/page_alloc.c +++ b/xen/common/page_alloc.c @@ -166,7 +166,15 @@ enum bootscrub_mode { BOOTSCRUB_ON, BOOTSCRUB_IDLE, }; -static enum bootscrub_mode __initdata opt_bootscrub = BOOTSCRUB_IDLE; + +/* + * opt_bootscrub should live in the init section, since it's not accessed + * afterwards. However at least LLVM assumes there are no side effects of + * accessing the variable, and optimizes the condition in init_heap_pages() so + * opt_bootscrub is read regardless of the value of system_state: + * https://bugs.llvm.org/show_bug.cgi?id=39707 + */ +static enum bootscrub_mode __read_mostly opt_bootscrub = BOOTSCRUB_IDLE; static int __init parse_bootscrub_param(const char *s) { /* Interpret 'bootscrub' alone in its positive boolean form */