Merge branch 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...

[firefly-linux-kernel-4.4.55.git] / arch / x86 / include / asm / thread_info.h

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 1d4e4f279a3281e094684ad29bd4b544d37af6ab..ea2dbe82cba3a74e06e269655cdfca8a67253e52 100644 (file)
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -12,6 +12,33 @@
 #include <asm/percpu.h>
 #include <asm/types.h>
 
+/*
+ * TOP_OF_KERNEL_STACK_PADDING is a number of unused bytes that we
+ * reserve at the top of the kernel stack.  We do it because of a nasty
+ * 32-bit corner case.  On x86_32, the hardware stack frame is
+ * variable-length.  Except for vm86 mode, struct pt_regs assumes a
+ * maximum-length frame.  If we enter from CPL 0, the top 8 bytes of
+ * pt_regs don't actually exist.  Ordinarily this doesn't matter, but it
+ * does in at least one case:
+ *
+ * If we take an NMI early enough in SYSENTER, then we can end up with
+ * pt_regs that extends above sp0.  On the way out, in the espfix code,
+ * we can read the saved SS value, but that value will be above sp0.
+ * Without this offset, that can result in a page fault.  (We are
+ * careful that, in this case, the value we read doesn't matter.)
+ *
+ * In vm86 mode, the hardware frame is much longer still, but we neither
+ * access the extra members from NMI context, nor do we write such a
+ * frame at sp0 at all.
+ *
+ * x86_64 has a fixed-length stack frame.
+ */
+#ifdef CONFIG_X86_32
+# define TOP_OF_KERNEL_STACK_PADDING 8
+#else
+# define TOP_OF_KERNEL_STACK_PADDING 0
+#endif
+
 /*
  * low level task data that entry.S needs immediate access to
  * - this struct should fit entirely inside of one cache line
@@ -145,7 +172,6 @@ struct thread_info {
 #define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW)
 
 #define STACK_WARN             (THREAD_SIZE/8)
-#define KERNEL_STACK_OFFSET    (5*(BITS_PER_LONG/8))
 
 /*
  * macros/functions for gaining access to the thread information structure
@@ -158,10 +184,7 @@ DECLARE_PER_CPU(unsigned long, kernel_stack);
 
 static inline struct thread_info *current_thread_info(void)
 {
-       struct thread_info *ti;
-       ti = (void *)(this_cpu_read_stable(kernel_stack) +
-                     KERNEL_STACK_OFFSET - THREAD_SIZE);
-       return ti;
+       return (struct thread_info *)(current_top_of_stack() - THREAD_SIZE);
 }
 
 static inline unsigned long current_stack_pointer(void)
@@ -177,16 +200,37 @@ static inline unsigned long current_stack_pointer(void)
 
 #else /* !__ASSEMBLY__ */
 
-/* how to get the thread information struct from ASM */
+/* Load thread_info address into "reg" */
 #define GET_THREAD_INFO(reg) \
        _ASM_MOV PER_CPU_VAR(kernel_stack),reg ; \
-       _ASM_SUB $(THREAD_SIZE-KERNEL_STACK_OFFSET),reg ;
+       _ASM_SUB $(THREAD_SIZE),reg ;
 
 /*
- * Same if PER_CPU_VAR(kernel_stack) is, perhaps with some offset, already in
- * a certain register (to be used in assembler memory operands).
+ * ASM operand which evaluates to a 'thread_info' address of
+ * the current task, if it is known that "reg" is exactly "off"
+ * bytes below the top of the stack currently.
+ *
+ * ( The kernel stack's size is known at build time, it is usually
+ *   2 or 4 pages, and the bottom  of the kernel stack contains
+ *   the thread_info structure. So to access the thread_info very
+ *   quickly from assembly code we can calculate down from the
+ *   top of the kernel stack to the bottom, using constant,
+ *   build-time calculations only. )
+ *
+ * For example, to fetch the current thread_info->flags value into %eax
+ * on x86-64 defconfig kernels, in syscall entry code where RSP is
+ * currently at exactly SIZEOF_PTREGS bytes away from the top of the
+ * stack:
+ *
+ *      mov ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS), %eax
+ *
+ * will translate to:
+ *
+ *      8b 84 24 b8 c0 ff ff      mov    -0x3f48(%rsp), %eax
+ *
+ * which is below the current RSP by almost 16K.
  */
-#define THREAD_INFO(reg, off) KERNEL_STACK_OFFSET+(off)-THREAD_SIZE(reg)
+#define ASM_THREAD_INFO(field, reg, off) ((field)+(off)-THREAD_SIZE)(reg)
 
 #endif
 
@@ -236,6 +280,16 @@ static inline bool is_ia32_task(void)
 #endif
        return false;
 }
+
+/*
+ * Force syscall return via IRET by making it look as if there was
+ * some work pending. IRET is our most capable (but slowest) syscall
+ * return path, which is able to restore modified SS, CS and certain
+ * EFLAGS values that other (fast) syscall return instructions
+ * are not able to restore properly.
+ */
+#define force_iret() set_thread_flag(TIF_NOTIFY_RESUME)
+
 #endif /* !__ASSEMBLY__ */
 
 #ifndef __ASSEMBLY__