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

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Date:   Thu, 28 Jan 2021 00:32:18 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Joerg Roedel <jroedel@...e.de>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        Kees Cook <keescook@...omium.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Jens Axboe <axboe@...nel.dk>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Brian Gerst <brgerst@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Mike Rapoport <rppt@...nel.org>, Mike Hommey <mh@...ndium.org>,
        Mark Gross <mgross@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Anthony Steinhauser <asteinhauser@...gle.com>,
        Jay Lang <jaytlang@....edu>,
        "Chang S. Bae" <chang.seok.bae@...el.com>
Subject: [PATCH V3 2/6] x86_32: use percpu instead of offset-calculation to get thread.sp0 when SWITCH_TO_KERNEL_STACK

From: Lai Jiangshan <laijs@...ux.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@...ux.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