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Date: Tue, 25 Feb 2020 23:47:34 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
Brian Gerst <brgerst@...il.com>,
Juergen Gross <jgross@...e.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Arnd Bergmann <arnd@...db.de>
Subject: [patch 15/15] x86/entry: Use return_from_exception()
Replace the ASM return from exception checks for user mode and kernel mode
return with the new C function and invoke this from the idtentry_exit()
helper for all regular exceptions and IST exceptions which hit user mode.
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
arch/x86/entry/common.c | 13 +++----------
arch/x86/entry/entry_32.S | 25 ++++---------------------
arch/x86/entry/entry_64.S | 25 ++-----------------------
arch/x86/include/asm/idtentry.h | 7 +++++--
4 files changed, 14 insertions(+), 56 deletions(-)
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -196,7 +196,7 @@ static void exit_to_usermode_loop(struct
}
/* Called with IRQs disabled. */
-static inline void __prepare_exit_to_usermode(struct pt_regs *regs)
+static inline void prepare_exit_to_usermode(struct pt_regs *regs)
{
struct thread_info *ti = current_thread_info();
u32 cached_flags;
@@ -241,13 +241,6 @@ static inline void __prepare_exit_to_use
mds_user_clear_cpu_buffers();
}
-__visible inline notrace void prepare_exit_to_usermode(struct pt_regs *regs)
-{
- __prepare_exit_to_usermode(regs);
- trace_hardirqs_on();
-}
-NOKPROBE_SYMBOL(prepare_exit_to_usermode);
-
#define SYSCALL_EXIT_WORK_FLAGS \
(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
_TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
@@ -299,7 +292,7 @@ static void syscall_slow_exit_work(struc
syscall_slow_exit_work(regs, cached_flags);
local_irq_disable();
- __prepare_exit_to_usermode(regs);
+ prepare_exit_to_usermode(regs);
/* Return to user space enables interrupts */
trace_hardirqs_on();
}
@@ -429,7 +422,7 @@ static __always_inline long do_fast_sysc
/* User code screwed up. */
local_irq_disable();
regs->ax = -EFAULT;
- __prepare_exit_to_usermode(regs);
+ prepare_exit_to_usermode(regs);
return 0; /* Keep it simple: use IRET. */
}
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -862,15 +862,10 @@ SYM_CODE_START(ret_from_fork)
SYM_CODE_END(ret_from_fork)
/*
- * Return to user mode is not as complex as all this looks,
- * but we want the default path for a system call return to
- * go as quickly as possible which is why some of this is
- * less clear than it otherwise should be.
+ * C code already did all preparatory work (prepare_exit_to_usermode or
+ * kernel preemption) so this just has to select the proper return path.
*/
-
- # userspace resumption stub bypassing syscall exit tracing
SYM_CODE_START_LOCAL(ret_from_exception)
-ret_from_intr:
#ifdef CONFIG_VM86
movl PT_EFLAGS(%esp), %eax # mix EFLAGS and CS
movb PT_CS(%esp), %al
@@ -884,9 +879,6 @@ SYM_CODE_START_LOCAL(ret_from_exception)
#endif
cmpl $USER_RPL, %eax
jb restore_all_kernel # not returning to v8086 or userspace
-
- movl %esp, %eax
- call prepare_exit_to_usermode
jmp restore_all_switch_stack
SYM_CODE_END(ret_from_exception)
@@ -1125,15 +1117,6 @@ SYM_FUNC_START(entry_INT80_32)
INTERRUPT_RETURN
restore_all_kernel:
-#ifdef CONFIG_PREEMPTION
- cmpl $0, PER_CPU_VAR(__preempt_count)
- jnz .Lno_preempt
- testl $X86_EFLAGS_IF, PT_EFLAGS(%esp) # interrupts off (exception path) ?
- jz .Lno_preempt
- call preempt_schedule_irq
-.Lno_preempt:
-#endif
- TRACE_IRQS_IRET
PARANOID_EXIT_TO_KERNEL_MODE
BUG_IF_WRONG_CR3
RESTORE_REGS 4
@@ -1247,7 +1230,7 @@ SYM_CODE_START_LOCAL(asm_\cfunc)
movl PT_ORIG_EAX(%esp), %edx /* get the vector from stack */
movl $-1, PT_ORIG_EAX(%esp) /* no syscall to restart */
call \cfunc
- jmp ret_from_intr
+ jmp ret_from_exception
SYM_CODE_END(asm_\cfunc)
.endm
@@ -1294,7 +1277,7 @@ SYM_FUNC_START(exc_xen_hypervisor_callba
#ifndef CONFIG_PREEMPTION
call xen_maybe_preempt_hcall
#endif
- jmp ret_from_intr
+ jmp ret_from_exception
SYM_FUNC_END(exc_xen_hypervisor_callback)
/*
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -701,10 +701,6 @@ SYM_CODE_END(\asmsym)
#include <asm/idtentry.h>
SYM_CODE_START_LOCAL(common_interrupt_return)
- /* Interrupt came from user space */
-.Lretint_user:
- mov %rsp,%rdi
- call prepare_exit_to_usermode
SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
#ifdef CONFIG_DEBUG_ENTRY
@@ -746,24 +742,7 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_
SWAPGS
INTERRUPT_RETURN
-
/* Returning to kernel space */
-retint_kernel:
-#ifdef CONFIG_PREEMPTION
- /* Interrupts are off */
- /* Check if we need preemption */
- btl $9, EFLAGS(%rsp) /* were interrupts off? */
- jnc 1f
- cmpl $0, PER_CPU_VAR(__preempt_count)
- jnz 1f
- call preempt_schedule_irq
-1:
-#endif
- /*
- * The iretq could re-enable interrupts:
- */
- TRACE_IRQS_IRETQ
-
SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL)
#ifdef CONFIG_DEBUG_ENTRY
/* Assert that pt_regs indicates kernel mode. */
@@ -1167,8 +1146,8 @@ SYM_CODE_START_LOCAL(error_exit)
UNWIND_HINT_REGS
DEBUG_ENTRY_ASSERT_IRQS_OFF
testb $3, CS(%rsp)
- jz retint_kernel
- jmp .Lretint_user
+ jz restore_regs_and_return_to_kernel
+ jmp swapgs_restore_regs_and_return_to_usermode
SYM_CODE_END(error_exit)
/*
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -41,11 +41,14 @@ static __always_inline void idtentry_ent
/**
* idtentry_exit - Prepare returning to low level ASM code
*
- * Disables interrupts before returning
+ * Invokes return_from_exception() which disables interrupts
+ * and handles return to user mode work and kernel preemption.
+ * This function returns with interrupts disabled and the
+ * hardirq tracing state updated.
*/
static __always_inline void idtentry_exit(struct pt_regs *regs)
{
- local_irq_disable();
+ return_from_exception(regs);
}
/**
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