[PATCH v4 12/17] x86/asm/entry/64: Save all regs on interrupt entry

Andy Lutomirski
2015-06-29T19:37:38Z

To prepare for the big rewrite of the error and interrupt exit
paths, we will need pt_regs completely filled in. It's already
completely filled in when error_exit runs, so rearrange interrupt
handling to match it. This will slow down interrupt handling very
slightly (eight instructions), but the simplification it enables
will be more than worth it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/entry/entry_64.S | 29 +++++++++--------------------
1 file changed, 9 insertions(+), 20 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 9bc76766aa71..51d34fafe4c0 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -502,21 +502,13 @@ END(irq_entries_start)
/* 0(%rsp): ~(interrupt number) */
.macro interrupt func
cld
- /*
- * Since nothing in interrupt handling code touches r12...r15 members
- * of "struct pt_regs", and since interrupts can nest, we can save
- * four stack slots and simultaneously provide
- * an unwind-friendly stack layout by saving "truncated" pt_regs
- * exactly up to rbp slot, without these members.
- */
- ALLOC_PT_GPREGS_ON_STACK -RBP
- SAVE_C_REGS -RBP
- /* this goes to 0(%rsp) for unwinder, not for saving the value: */
- SAVE_EXTRA_REGS_RBP -RBP
+ ALLOC_PT_GPREGS_ON_STACK
+ SAVE_C_REGS
+ SAVE_EXTRA_REGS

- leaq -RBP(%rsp), %rdi /* arg1 for \func (pointer to pt_regs) */
+ movq %rsp,%rdi /* arg1 for \func (pointer to pt_regs) */

- testb $3, CS-RBP(%rsp)
+ testb $3, CS(%rsp)
jz 1f
SWAPGS
1:
@@ -553,9 +545,7 @@ ret_from_intr:
decl PER_CPU_VAR(irq_count)

/* Restore saved previous stack */
- popq %rsi
- /* return code expects complete pt_regs - adjust rsp accordingly: */
- leaq -RBP(%rsi), %rsp
+ popq %rsp

testb $3, CS(%rsp)
jz retint_kernel
@@ -580,7 +570,7 @@ retint_swapgs: /* return to user-space */
TRACE_IRQS_IRETQ

SWAPGS
- jmp restore_c_regs_and_iret
+ jmp restore_regs_and_iret

/* Returning to kernel space */
retint_kernel:
@@ -604,6 +594,8 @@ retint_kernel:
* At this label, code paths which return to kernel and to user,
* which come from interrupts/exception and from syscalls, merge.
*/
+restore_regs_and_iret:
+ RESTORE_EXTRA_REGS
restore_c_regs_and_iret:
RESTORE_C_REGS
REMOVE_PT_GPREGS_FROM_STACK 8
@@ -674,12 +666,10 @@ retint_signal:
jz retint_swapgs
TRACE_IRQS_ON
ENABLE_INTERRUPTS(CLBR_NONE)
- SAVE_EXTRA_REGS
movq $-1, ORIG_RAX(%rsp)
xorl %esi, %esi /* oldset */
movq %rsp, %rdi /* &pt_regs */
call do_notify_resume
- RESTORE_EXTRA_REGS
DISABLE_INTERRUPTS(CLBR_NONE)
TRACE_IRQS_OFF
GET_THREAD_INFO(%rcx)
@@ -1160,7 +1150,6 @@ END(error_entry)
*/
ENTRY(error_exit)
movl %ebx, %eax
- RESTORE_EXTRA_REGS
DISABLE_INTERRUPTS(CLBR_NONE)
TRACE_IRQS_OFF
testl %eax, %eax
--
2.4.3