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From:   Lai Jiangshan <jiangshanlai@gmail.com>
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Subject: [PATCH V2 2/6] x86_32: use percpu instead of offset-calculation to get thread.sp0 when SWITCH_TO_KERNEL_STACK
Date:   Tue, 26 Jan 2021 01:34:30 +0800
Message-Id: <20210125173444.22696-3-jiangshanlai@gmail.com>
In-Reply-To: <20210125173444.22696-1-jiangshanlai@gmail.com>
References: <CALCETrWPnvNr9S2hsxL+pbhNWv0OOL7tBq1XmABPjYK7zZSJbw@mail.gmail.com>
 <20210125173444.22696-1-jiangshanlai@gmail.com>
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From: Lai Jiangshan <laijs@linux.alibaba.com>

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@linux.alibaba.com>
---
 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