[PATCH V3 2/6] x86_32: use percpu instead of offset-calculation to get thread.sp0 when SWITCH_TO_KERNEL_STACK

[Lai Jiangshan]

From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>

TSS_entry2task_stack is used to refer to tss.sp1 which is stored the value
of thread.sp0.

At the code where TSS_entry2task_stack is used in SWITCH_TO_KERNEL_STACK,
the CR3 is already kernel CR3 and kernel segments is loaded.

So we can directly use the percpu to get tss.sp1(thread.sp0) instead of
the complex offset-calculation.

Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
 arch/x86/entry/entry_32.S | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index df8c017e6161..3b4d1a63d1f0 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -465,16 +465,11 @@
 	cmpl	$SIZEOF_entry_stack, %ecx
 	jae	.Lend_\@
 
-	/* Load stack pointer into %esi and %edi */
+	/* Load stack pointer into %esi */
 	movl	%esp, %esi
-	movl	%esi, %edi
-
-	/* Move %edi to the top of the entry stack */
-	andl	$(MASK_entry_stack), %edi
-	addl	$(SIZEOF_entry_stack), %edi
 
 	/* Load top of task-stack into %edi */
-	movl	TSS_entry2task_stack(%edi), %edi
+	movl	PER_CPU_VAR(cpu_tss_rw + TSS_sp1), %edi
 
 	/* Special case - entry from kernel mode via entry stack */
 #ifdef CONFIG_VM86
-- 
2.19.1.6.gb485710b