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From:   Lai Jiangshan <jiangshanlai@gmail.com>
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Cc:     Lai Jiangshan <laijs@linux.alibaba.com>,
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Subject: [PATCH V2 5/6] x86_32/sysenter: use percpu to get thread.sp0 when sysenter
Date:   Tue, 26 Jan 2021 01:34:33 +0800
Message-Id: <20210125173444.22696-6-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 sysenter, the CR3 is
already kernel CR3 and kernel segments is loaded.

So that we can directly use percpu for it instead of offset-calculation.

And we remove the unused TSS_entry2task_stack.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_32.S        |  2 +-
 arch/x86/kernel/asm-offsets_32.c | 10 ----------
 2 files changed, 1 insertion(+), 11 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index a8d2640394f9..3cb42efb3c04 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -916,7 +916,7 @@ SYM_FUNC_START(entry_SYSENTER_32)
 
 	/* Switch to task stack */
 	movl	%esp, %eax
-	movl	(3*4+TSS_entry2task_stack)(%esp), %esp
+	movl	PER_CPU_VAR(cpu_tss_rw + TSS_sp1), %esp
 
 .Lsysenter_past_esp:
 	pushl	$__USER_DS		/* pt_regs->ss */
diff --git a/arch/x86/kernel/asm-offsets_32.c b/arch/x86/kernel/asm-offsets_32.c
index 6e043f295a60..6d4143cfbf03 100644
--- a/arch/x86/kernel/asm-offsets_32.c
+++ b/arch/x86/kernel/asm-offsets_32.c
@@ -43,16 +43,6 @@ void foo(void)
 	OFFSET(saved_context_gdt_desc, saved_context, gdt_desc);
 	BLANK();
 
-	/*
-	 * Offset from the entry stack to task stack stored in TSS. Kernel entry
-	 * happens on the per-cpu entry-stack, and the asm code switches to the
-	 * task-stack pointer stored in x86_tss.sp1, which is a copy of
-	 * task->thread.sp0 where entry code can find it.
-	 */
-	DEFINE(TSS_entry2task_stack,
-	       offsetof(struct cpu_entry_area, tss.x86_tss.sp1) -
-	       offsetofend(struct cpu_entry_area, entry_stack_page.stack));
-
 #ifdef CONFIG_STACKPROTECTOR
 	BLANK();
 	OFFSET(stack_canary_offset, stack_canary, canary);
-- 
2.19.1.6.gb485710b