From mboxrd@z Thu Jan 1 00:00:00 1970 From: achandran@mvista.com (Arun Chandran) Date: Wed, 13 Aug 2014 17:24:41 +0530 Subject: [PATCH] Arm64: convert part of soft_restart() to assembly Message-ID: <1407930881-533-1-git-send-email-achandran@mvista.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org The current soft_restart() and setup_restart implementations incorrectly assume that compiler will not spill/fill values to/from stack. However this assumption seems to be wrong, revealed by the disassembly of the currently existing code (v3.16) built with Linaro GCC 4.9-2014.05. ffffffc000085224 : ffffffc000085224: a9be7bfd stp x29, x30, [sp,#-32]! ffffffc000085228: 910003fd mov x29, sp ffffffc00008522c: f9000fa0 str x0, [x29,#24] ffffffc000085230: 94003d21 bl ffffffc0000946b4 ffffffc000085234: 94003b33 bl ffffffc000093f00 ffffffc000085238: 94003dfa bl ffffffc000094a20 ffffffc00008523c: 94003b31 bl ffffffc000093f00 ffffffc000085240: b0003321 adrp x1, ffffffc0006ea000 ffffffc000085244: f9400fa0 ldr x0, [x29,#24] ----> spilled addr ffffffc000085248: f942fc22 ldr x2, [x1,#1528] ----> spilled memstart_addr ffffffc00008524c: f0000061 adrp x1, ffffffc000094000 <__inval_cache_range+0x40> ffffffc000085250: 91290021 add x1, x1, #0xa40 ffffffc000085254: 8b010041 add x1, x2, x1 ffffffc000085258: d2c00802 mov x2, #0x4000000000 // #274877906944 ffffffc00008525c: 8b020021 add x1, x1, x2 ffffffc000085260: d63f0020 blr x1 ... The compiler is clearly spilling here around the cache being disabled, resulting in stale values being restored. As we cannot control the compiler's spilling behaviour we must rewrite the functions in assembly to avoid use of the stack. Signed-off-by: Arun Chandran --- arch/arm64/include/asm/proc-fns.h | 2 ++ arch/arm64/kernel/process.c | 30 ++---------------------------- arch/arm64/mm/proc.S | 14 ++++++++++++++ 3 files changed, 18 insertions(+), 28 deletions(-) diff --git a/arch/arm64/include/asm/proc-fns.h b/arch/arm64/include/asm/proc-fns.h index 0c657bb..86be4f9 100644 --- a/arch/arm64/include/asm/proc-fns.h +++ b/arch/arm64/include/asm/proc-fns.h @@ -32,6 +32,8 @@ extern void cpu_cache_off(void); extern void cpu_do_idle(void); extern void cpu_do_switch_mm(unsigned long pgd_phys, struct mm_struct *mm); extern void cpu_reset(unsigned long addr) __attribute__((noreturn)); +extern void cpu_soft_restart(phys_addr_t cpu_reset, + unsigned long addr) __attribute__((noreturn)); extern void cpu_do_suspend(struct cpu_suspend_ctx *ptr); extern u64 cpu_do_resume(phys_addr_t ptr, u64 idmap_ttbr); diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 1309d64..bf66922 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -57,36 +57,10 @@ unsigned long __stack_chk_guard __read_mostly; EXPORT_SYMBOL(__stack_chk_guard); #endif -static void setup_restart(void) -{ - /* - * Tell the mm system that we are going to reboot - - * we may need it to insert some 1:1 mappings so that - * soft boot works. - */ - setup_mm_for_reboot(); - - /* Clean and invalidate caches */ - flush_cache_all(); - - /* Turn D-cache off */ - cpu_cache_off(); - - /* Push out any further dirty data, and ensure cache is empty */ - flush_cache_all(); -} - void soft_restart(unsigned long addr) { - typedef void (*phys_reset_t)(unsigned long); - phys_reset_t phys_reset; - - setup_restart(); - - /* Switch to the identity mapping */ - phys_reset = (phys_reset_t)virt_to_phys(cpu_reset); - phys_reset(addr); - + setup_mm_for_reboot(); + cpu_soft_restart(virt_to_phys(cpu_reset), addr); /* Should never get here */ BUG(); } diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S index 7736779..0eff5ee 100644 --- a/arch/arm64/mm/proc.S +++ b/arch/arm64/mm/proc.S @@ -76,6 +76,20 @@ ENTRY(cpu_reset) ret x0 ENDPROC(cpu_reset) +ENTRY(cpu_soft_restart) + /* Save address of cpu_reset() and reset address */ + mov x19, x0 + mov x20, x1 + + /* Turn D-cache off */ + bl cpu_cache_off + /* Push out all dirty data, and ensure cache is empty */ + bl flush_cache_all + + mov x0, x20 + ret x19 +ENDPROC(cpu_soft_restart) + /* * cpu_do_idle() * -- 1.7.9.5