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Message-ID: <20240617084516.1484390-4-xin@zytor.com>
Date: Mon, 17 Jun 2024 01:45:15 -0700
From: "Xin Li (Intel)" <xin@...or.com>
To: linux-kernel@...r.kernel.org
Cc: luto@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
peterz@...radead.org, brgerst@...il.com
Subject: [PATCH v1 3/3] x86: Get rid of TOP_OF_KERNEL_STACK_PADDING on x86_64
Because task_pt_regs() is now just an alias of thread_info.user_pt_regs,
and no matter whether FRED is enabled or not a user level event frame on
x86_64 is always pushed from top of current task kernel stack, i.e.,
'(unsigned long)task_stack_page(task) + THREAD_SIZE', there is no meaning
to keep TOP_OF_KERNEL_STACK_PADDING on x86_64, thus remove it.
Signed-off-by: Xin Li (Intel) <xin@...or.com>
---
arch/x86/include/asm/processor.h | 6 ++++--
arch/x86/include/asm/switch_to.h | 2 +-
arch/x86/include/asm/thread_info.h | 10 ----------
arch/x86/kernel/process.c | 3 +--
4 files changed, 6 insertions(+), 15 deletions(-)
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 91803844c4d7..9c5294f6d923 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -644,8 +644,6 @@ extern unsigned long __end_init_stack[];
*/
#define TOP_OF_INIT_STACK ((unsigned long)&__end_init_stack)
-#define task_top_of_stack(task) ((unsigned long)(task_pt_regs(task) + 1))
-
/*
* task_pt_regs() no longer converts a fixed offset from top of a task
* kernel stack to a pt_regs structure pointer, but rather returns
@@ -660,6 +658,9 @@ extern unsigned long __end_init_stack[];
#define task_pt_regs(task) ((task)->thread_info.user_pt_regs)
#ifdef CONFIG_X86_32
+#define task_top_of_stack(task) ((unsigned long)task_stack_page(task) + THREAD_SIZE \
+ - TOP_OF_KERNEL_STACK_PADDING)
+
#define INIT_THREAD { \
.sp0 = TOP_OF_INIT_STACK, \
.sysenter_cs = __KERNEL_CS, \
@@ -669,6 +670,7 @@ extern unsigned long __end_init_stack[];
#else
extern unsigned long __top_init_kernel_stack[];
+#define task_top_of_stack(task) ((unsigned long)task_stack_page(task) + THREAD_SIZE)
#define INIT_THREAD { \
.sp = (unsigned long)&__top_init_kernel_stack, \
diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index c3bd0c0758c9..902f1612ef3f 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -72,7 +72,7 @@ static inline void update_task_stack(struct task_struct *task)
#else
if (cpu_feature_enabled(X86_FEATURE_FRED)) {
/* WRMSRNS is a baseline feature for FRED. */
- wrmsrns(MSR_IA32_FRED_RSP0, (unsigned long)task_stack_page(task) + THREAD_SIZE);
+ wrmsrns(MSR_IA32_FRED_RSP0, task_top_of_stack(task));
} else if (cpu_feature_enabled(X86_FEATURE_XENPV)) {
/* Xen PV enters the kernel on the thread stack. */
load_sp0(task_top_of_stack(task));
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 326268d440cf..331a6f32a0be 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -30,10 +30,6 @@
*
* In vm86 mode, the hardware frame is much longer still, so add 16
* bytes to make room for the real-mode segments.
- *
- * x86-64 has a fixed-length stack frame, but it depends on whether
- * or not FRED is enabled. Future versions of FRED might make this
- * dynamic, but for now it is always 2 words longer.
*/
#ifdef CONFIG_X86_32
# ifdef CONFIG_VM86
@@ -41,12 +37,6 @@
# else
# define TOP_OF_KERNEL_STACK_PADDING 8
# endif
-#else /* x86-64 */
-# ifdef CONFIG_X86_FRED
-# define TOP_OF_KERNEL_STACK_PADDING (2 * 8)
-# else
-# define TOP_OF_KERNEL_STACK_PADDING 0
-# endif
#endif
/*
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 787a402e4ead..99f9887f710e 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -116,9 +116,8 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
*/
void arch_init_user_pt_regs(struct task_struct *tsk)
{
- unsigned long top_of_stack = (unsigned long)task_stack_page(tsk) + THREAD_SIZE;
+ unsigned long top_of_stack = task_top_of_stack(tsk);
- top_of_stack -= TOP_OF_KERNEL_STACK_PADDING;
tsk->thread_info.user_pt_regs = (struct pt_regs *)top_of_stack - 1;
}
--
2.45.1
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