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Subject[PATCH V4 4/6] x86/entry/32: Restore %fs before switching stack
Date
From: Lai Jiangshan <laijs@linux.alibaba.com>

entry_SYSENTER_32 saves the user %fs in the entry stack and restores the
kernel %fs before loading the task stack for stack switching, so that it
can use percpu before switching stack in the next patch.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/entry/entry_32.S | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 3e693db0963d..01f098c5b017 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -279,11 +279,13 @@
.Lfinished_frame_\@:
.endm

-.macro SAVE_ALL pt_regs_ax=%eax switch_stacks=0 skip_gs=0 unwind_espfix=0
+.macro SAVE_ALL pt_regs_ax=%eax switch_stacks=0 skip_gs=0 skip_fs=0 unwind_espfix=0
cld
.if \skip_gs == 0
PUSH_GS
.endif
+
+.if \skip_fs == 0
pushl %fs

pushl %eax
@@ -293,6 +295,7 @@
UNWIND_ESPFIX_STACK
.endif
popl %eax
+.endif

FIXUP_FRAME
pushl %es
@@ -906,18 +909,27 @@ SYM_FUNC_START(entry_SYSENTER_32)
BUG_IF_WRONG_CR3 no_user_check=1
SWITCH_TO_KERNEL_CR3 scratch_reg=%eax

+ /* Restore kernel %fs, so that we can use PERCPU */
+ pushl %fs
+ movl $(__KERNEL_PERCPU), %eax
+ movl %eax, %fs
+
/* Switch to task stack */
movl %esp, %eax
- movl (2*4+TSS_entry2task_stack)(%esp), %esp
+ movl (3*4+TSS_entry2task_stack)(%esp), %esp

.Lsysenter_past_esp:
pushl $__USER_DS /* pt_regs->ss */
pushl $0 /* pt_regs->sp (placeholder) */
- pushl %ss:4(%eax) /* pt_regs->flags (except IF = 0) */
+ pushl %ss:8(%eax) /* pt_regs->flags (except IF = 0) */
pushl $__USER_CS /* pt_regs->cs */
pushl $0 /* pt_regs->ip = 0 (placeholder) */
- pushl %ss:(%eax) /* pt_regs->orig_ax */
- SAVE_ALL pt_regs_ax=$-ENOSYS /* save rest, stack already switched */
+ pushl %ss:4(%eax) /* pt_regs->orig_ax */
+ PUSH_GS /* pt_regs->gs */
+ pushl %ss:(%eax) /* pt_regs->fs */
+ /* save rest, stack and %fs already switched */
+ SAVE_ALL pt_regs_ax=$-ENOSYS skip_gs=1 skip_fs=1
+ SET_KERNEL_GS %edx

/*
* SYSENTER doesn't filter flags, so we need to clear NT, AC
--
2.19.1.6.gb485710b
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