[PATCH] i386: Convert PDA into the percpu section

Currently x86 (similar to x84-64) has a special per-cpu structure
called "i386_pda" which can be easily and efficiently referenced via
the %fs register.  An ELF section is more flexible than a structure,
allowing any piece of code to use this area.  Indeed, such a section
already exists: the per-cpu area.

So this patch:
(1) Removes the PDA and uses per-cpu variables for each current member.
(2) Replaces the __KERNEL_PDA segment with __KERNEL_PERCPU.
(3) Creates a per-cpu mirror of __per_cpu_offset called this_cpu_off, which
    can be used to calculate addresses for this CPU's variables.
(4) Simplifies startup, because %fs doesn't need to be loaded with a
    special segment at early boot; it can be deferred until the first
    percpu area is allocated (or never for UP).

The result is less code and one less x86-specific concept.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Andi Kleen <ak@suse.de>

1 files changed, 123 insertions, 9 deletions

diff --git a/include/asm-i386/percpu.h b/include/asm-i386/percpu.h
index a10e7c68ae9d..c5f12f0d9c23 100644
--- a/include/asm-i386/percpu.h
+++ b/include/asm-i386/percpu.h
@@ -1,9 +1,30 @@
 #ifndef __ARCH_I386_PERCPU__
 #define __ARCH_I386_PERCPU__
 
-#ifndef __ASSEMBLY__
-#include <asm-generic/percpu.h>
-#else
+#ifdef __ASSEMBLY__
+
+/*
+ * PER_CPU finds an address of a per-cpu variable.
+ *
+ * Args:
+ *    var - variable name
+ *    reg - 32bit register
+ *
+ * The resulting address is stored in the "reg" argument.
+ *
+ * Example:
+ *    PER_CPU(cpu_gdt_descr, %ebx)
+ */
+#ifdef CONFIG_SMP
+#define PER_CPU(var, reg)                       \
+        movl %fs:per_cpu__this_cpu_off, reg;            \
+        addl $per_cpu__##var, reg
+#else /* ! SMP */
+#define PER_CPU(var, reg) \
+        movl $per_cpu__##var, reg;
+#endif  /* SMP */
+
+#else /* ...!ASSEMBLY */
 
 /*
  * PER_CPU finds an address of a per-cpu variable.
@@ -18,14 +39,107 @@
  *    PER_CPU(cpu_gdt_descr, %ebx)
  */
 #ifdef CONFIG_SMP
-#define PER_CPU(var, cpu) \
-        movl __per_cpu_offset(,cpu,4), cpu;     \
-        addl $per_cpu__##var, cpu;
-#else /* ! SMP */
-#define PER_CPU(var, cpu) \
-        movl $per_cpu__##var, cpu;
+/* Same as generic implementation except for optimized local access. */
+#define __GENERIC_PER_CPU
+
+/* This is used for other cpus to find our section. */
+extern unsigned long __per_cpu_offset[];
+
+/* Separate out the type, so (int[3], foo) works. */
+#define DECLARE_PER_CPU(type, name) extern __typeof__(type) per_cpu__##name
+#define DEFINE_PER_CPU(type, name) \
+    __attribute__((__section__(".data.percpu"))) __typeof__(type) per_cpu__##name
+
+/* We can use this directly for local CPU (faster). */
+DECLARE_PER_CPU(unsigned long, this_cpu_off);
+
+/* var is in discarded region: offset to particular copy we want */
+#define per_cpu(var, cpu) (*({                          \
+        extern int simple_indentifier_##var(void);      \
+        RELOC_HIDE(&per_cpu__##var, __per_cpu_offset[cpu]); }))
+
+#define __raw_get_cpu_var(var) (*({                                     \
+        extern int simple_indentifier_##var(void);                      \
+        RELOC_HIDE(&per_cpu__##var, x86_read_percpu(this_cpu_off));     \
+}))
+
+#define __get_cpu_var(var) __raw_get_cpu_var(var)
+
+/* A macro to avoid #include hell... */
+#define percpu_modcopy(pcpudst, src, size)                      \
+do {                                                            \
+        unsigned int __i;                                       \
+        for_each_possible_cpu(__i)                              \
+                memcpy((pcpudst)+__per_cpu_offset[__i],         \
+                       (src), (size));                          \
+} while (0)
+
+#define EXPORT_PER_CPU_SYMBOL(var) EXPORT_SYMBOL(per_cpu__##var)
+#define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(per_cpu__##var)
+
+/* fs segment starts at (positive) offset == __per_cpu_offset[cpu] */
+#define __percpu_seg "%%fs:"
+#else  /* !SMP */
+#include <asm-generic/percpu.h>
+#define __percpu_seg ""
 #endif  /* SMP */
 
+/* For arch-specific code, we can use direct single-insn ops (they
+ * don't give an lvalue though). */
+extern void __bad_percpu_size(void);
+
+#define percpu_to_op(op,var,val)                                \
+        do {                                                    \
+                typedef typeof(var) T__;                        \
+                if (0) { T__ tmp__; tmp__ = (val); }            \
+                switch (sizeof(var)) {                          \
+                case 1:                                         \
+                        asm(op "b %1,"__percpu_seg"%0"          \
+                            : "+m" (var)                        \
+                            :"ri" ((T__)val));                  \
+                        break;                                  \
+                case 2:                                         \
+                        asm(op "w %1,"__percpu_seg"%0"          \
+                            : "+m" (var)                        \
+                            :"ri" ((T__)val));                  \
+                        break;                                  \
+                case 4:                                         \
+                        asm(op "l %1,"__percpu_seg"%0"          \
+                            : "+m" (var)                        \
+                            :"ri" ((T__)val));                  \
+                        break;                                  \
+                default: __bad_percpu_size();                   \
+                }                                               \
+        } while (0)
+
+#define percpu_from_op(op,var)                                  \
+        ({                                                      \
+                typeof(var) ret__;                              \
+                switch (sizeof(var)) {                          \
+                case 1:                                         \
+                        asm(op "b "__percpu_seg"%1,%0"          \
+                            : "=r" (ret__)                      \
+                            : "m" (var));                       \
+                        break;                                  \
+                case 2:                                         \
+                        asm(op "w "__percpu_seg"%1,%0"          \
+                            : "=r" (ret__)                      \
+                            : "m" (var));                       \
+                        break;                                  \
+                case 4:                                         \
+                        asm(op "l "__percpu_seg"%1,%0"          \
+                            : "=r" (ret__)                      \
+                            : "m" (var));                       \
+                        break;                                  \
+                default: __bad_percpu_size();                   \
+                }                                               \
+                ret__; })
+
+#define x86_read_percpu(var) percpu_from_op("mov", per_cpu__##var)
+#define x86_write_percpu(var,val) percpu_to_op("mov", per_cpu__##var, val)
+#define x86_add_percpu(var,val) percpu_to_op("add", per_cpu__##var, val)
+#define x86_sub_percpu(var,val) percpu_to_op("sub", per_cpu__##var, val)
+#define x86_or_percpu(var,val) percpu_to_op("or", per_cpu__##var, val)
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __ARCH_I386_PERCPU__ */