[PATCH 03/11] x86/entry: Switch the stack after error_entry() returns

[Lai Jiangshan <jiangshanlai@xxxxxxxxx>]

From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>

error_entry() calls sync_regs() to settle/copy the pt_regs and switches
the stack directly after sync_regs().  But error_entry() itself is also
a function call, the switching has to handle the return address of it
together, which causes the work complicated and tangly.

Switching to the stack after error_entry() makes the code simpler and
intuitive.

Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
 arch/x86/entry/entry_64.S | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index f8faff3ca61e..6baa7413f7eb 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -323,6 +323,8 @@ SYM_CODE_END(ret_from_fork)
 .macro idtentry_body cfunc has_error_code:req
 
        call    error_entry
+       movq    %rax, %rsp                      /* switch stack settled by 
sync_regs() */
+       ENCODE_FRAME_POINTER
        UNWIND_HINT_REGS
 
        movq    %rsp, %rdi                      /* pt_regs pointer into 1st 
argument*/
@@ -981,14 +983,10 @@ SYM_CODE_START_LOCAL(error_entry)
        /* We have user CR3.  Change to kernel CR3. */
        SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
 
+       leaq    8(%rsp), %rdi                   /* arg0 = pt_regs pointer */
 .Lerror_entry_from_usermode_after_swapgs:
        /* Put us onto the real thread stack. */
-       popq    %r12                            /* save return addr in %12 */
-       movq    %rsp, %rdi                      /* arg0 = pt_regs pointer */
        call    sync_regs
-       movq    %rax, %rsp                      /* switch stack */
-       ENCODE_FRAME_POINTER
-       pushq   %r12
        ret
 
        /*
@@ -1020,6 +1018,7 @@ SYM_CODE_START_LOCAL(error_entry)
         */
 .Lerror_entry_done_lfence:
        FENCE_SWAPGS_KERNEL_ENTRY
+       leaq    8(%rsp), %rax                   /* return pt_regs pointer */
        ret
 
 .Lbstep_iret:
@@ -1040,12 +1039,9 @@ SYM_CODE_START_LOCAL(error_entry)
         * Pretend that the exception came from user mode: set up pt_regs
         * as if we faulted immediately after IRET.
         */
-       popq    %r12                            /* save return addr in %12 */
-       movq    %rsp, %rdi                      /* arg0 = pt_regs pointer */
+       leaq    8(%rsp), %rdi                   /* arg0 = pt_regs pointer */
        call    fixup_bad_iret
-       mov     %rax, %rsp
-       ENCODE_FRAME_POINTER
-       pushq   %r12
+       mov     %rax, %rdi
        jmp     .Lerror_entry_from_usermode_after_swapgs
 SYM_CODE_END(error_entry)
 
-- 
2.19.1.6.gb485710b