From baa745a3378046ca1c5477495df6ccbec7690428 Mon Sep 17 00:00:00 2001 From: Russell King Date: Sun, 7 Dec 2008 09:44:55 +0000 Subject: [PATCH] [ARM] Fix alignment fault handling for ARMv6 and later CPUs On ARMv6 and later CPUs, it is possible for userspace processes to get stuck on a misaligned load or store due to the "ignore fault" setting; unlike previous CPUs, retrying the instruction without the 'A' bit set does not always cause the load to succeed. We have no real option but to default to fixing up alignment faults on these CPUs, and having the CPU fix up those misaligned accesses which it can. Reported-by: Wolfgang Grandegger Signed-off-by: Russell King --- arch/arm/mm/alignment.c | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-) diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c index 133e65d166b..2d5884ce043 100644 --- a/arch/arm/mm/alignment.c +++ b/arch/arm/mm/alignment.c @@ -70,6 +70,10 @@ static unsigned long ai_dword; static unsigned long ai_multi; static int ai_usermode; +#define UM_WARN (1 << 0) +#define UM_FIXUP (1 << 1) +#define UM_SIGNAL (1 << 2) + #ifdef CONFIG_PROC_FS static const char *usermode_action[] = { "ignored", @@ -754,7 +758,7 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs) user: ai_user += 1; - if (ai_usermode & 1) + if (ai_usermode & UM_WARN) printk("Alignment trap: %s (%d) PC=0x%08lx Instr=0x%0*lx " "Address=0x%08lx FSR 0x%03x\n", current->comm, task_pid_nr(current), instrptr, @@ -762,10 +766,10 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs) thumb_mode(regs) ? tinstr : instr, addr, fsr); - if (ai_usermode & 2) + if (ai_usermode & UM_FIXUP) goto fixup; - if (ai_usermode & 4) + if (ai_usermode & UM_SIGNAL) force_sig(SIGBUS, current); else set_cr(cr_no_alignment); @@ -796,6 +800,22 @@ static int __init alignment_init(void) res->write_proc = proc_alignment_write; #endif + /* + * ARMv6 and later CPUs can perform unaligned accesses for + * most single load and store instructions up to word size. + * LDM, STM, LDRD and STRD still need to be handled. + * + * Ignoring the alignment fault is not an option on these + * CPUs since we spin re-faulting the instruction without + * making any progress. + */ + if (cpu_architecture() >= CPU_ARCH_ARMv6 && (cr_alignment & CR_U)) { + cr_alignment &= ~CR_A; + cr_no_alignment &= ~CR_A; + set_cr(cr_alignment); + ai_usermode = UM_FIXUP; + } + hook_fault_code(1, do_alignment, SIGILL, "alignment exception"); hook_fault_code(3, do_alignment, SIGILL, "alignment exception"); -- 2.20.1