ARM: Allow SMP kernels to boot on UP systems

UP systems do not implement all the instructions that SMP systems have,
so in order to boot a SMP kernel on a UP system, we need to rewrite
parts of the kernel.

Do this using an 'alternatives' scheme, where the kernel code and data
is modified prior to initialization to replace the SMP instructions,
thereby rendering the problematical code ineffectual.  We use the linker
to generate a list of 32-bit word locations and their replacement values,
and run through these replacements when we detect a UP system.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 27 insertions, 14 deletions

diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index 7563ff0141bd..df422fee1cb6 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -30,15 +30,13 @@
 #define TTB_IRGN_WT     ((1 << 0) | (0 << 6))
 #define TTB_IRGN_WB     ((1 << 0) | (1 << 6))
 
-#ifndef CONFIG_SMP
 /* PTWs cacheable, inner WB not shareable, outer WB not shareable */
-#define TTB_FLAGS       TTB_IRGN_WB|TTB_RGN_OC_WB
-#define PMD_FLAGS       PMD_SECT_WB
-#else
+#define TTB_FLAGS_UP    TTB_IRGN_WB|TTB_RGN_OC_WB
+#define PMD_FLAGS_UP    PMD_SECT_WB
+
 /* PTWs cacheable, inner WBWA shareable, outer WBWA not shareable */
-#define TTB_FLAGS       TTB_IRGN_WBWA|TTB_S|TTB_NOS|TTB_RGN_OC_WBWA
-#define PMD_FLAGS       PMD_SECT_WBWA|PMD_SECT_S
-#endif
+#define TTB_FLAGS_SMP   TTB_IRGN_WBWA|TTB_S|TTB_NOS|TTB_RGN_OC_WBWA
+#define PMD_FLAGS_SMP   PMD_SECT_WBWA|PMD_SECT_S
 
 ENTRY(cpu_v7_proc_init)
         mov     pc, lr
@@ -105,7 +103,8 @@ ENTRY(cpu_v7_switch_mm)
 #ifdef CONFIG_MMU
         mov     r2, #0
         ldr     r1, [r1, #MM_CONTEXT_ID]        @ get mm->context.id
-        orr     r0, r0, #TTB_FLAGS
+        ALT_SMP(orr     r0, r0, #TTB_FLAGS_SMP)
+        ALT_UP(orr      r0, r0, #TTB_FLAGS_UP)
 #ifdef CONFIG_ARM_ERRATA_430973
         mcr     p15, 0, r2, c7, c5, 6           @ flush BTAC/BTB
 #endif
@@ -188,7 +187,8 @@ cpu_v7_name:
  */
 __v7_ca9mp_setup:
 #ifdef CONFIG_SMP
-        mrc     p15, 0, r0, c1, c0, 1
+        ALT_SMP(mrc     p15, 0, r0, c1, c0, 1)
+        ALT_UP(mov      r0, #(1 << 6))          @ fake it for UP
         tst     r0, #(1 << 6)                   @ SMP/nAMP mode enabled?
         orreq   r0, r0, #(1 << 6) | (1 << 0)    @ Enable SMP/nAMP mode and
         mcreq   p15, 0, r0, c1, c0, 1           @ TLB ops broadcasting
@@ -262,7 +262,8 @@ __v7_setup:
 #ifdef CONFIG_MMU
         mcr     p15, 0, r10, c8, c7, 0          @ invalidate I + D TLBs
         mcr     p15, 0, r10, c2, c0, 2          @ TTB control register
-        orr     r4, r4, #TTB_FLAGS
+        ALT_SMP(orr     r4, r4, #TTB_FLAGS_SMP)
+        ALT_UP(orr      r4, r4, #TTB_FLAGS_UP)
         mcr     p15, 0, r4, c2, c0, 1           @ load TTB1
         mov     r10, #0x1f                      @ domains 0, 1 = manager
         mcr     p15, 0, r10, c3, c0, 0          @ load domain access register
@@ -354,10 +355,16 @@ cpu_elf_name:
 __v7_ca9mp_proc_info:
         .long   0x410fc090              @ Required ID value
         .long   0xff0ffff0              @ Mask for ID
-        .long   PMD_TYPE_SECT | \
+        ALT_SMP(.long \
+                PMD_TYPE_SECT | \
+                PMD_SECT_AP_WRITE | \
+                PMD_SECT_AP_READ | \
+                PMD_FLAGS_SMP)
+        ALT_UP(.long \
+                PMD_TYPE_SECT | \
                 PMD_SECT_AP_WRITE | \
                 PMD_SECT_AP_READ | \
-                PMD_FLAGS
+                PMD_FLAGS_UP)
         .long   PMD_TYPE_SECT | \
                 PMD_SECT_XN | \
                 PMD_SECT_AP_WRITE | \
@@ -380,10 +387,16 @@ __v7_ca9mp_proc_info:
 __v7_proc_info:
         .long   0x000f0000              @ Required ID value
         .long   0x000f0000              @ Mask for ID
-        .long   PMD_TYPE_SECT | \
+        ALT_SMP(.long \
+                PMD_TYPE_SECT | \
+                PMD_SECT_AP_WRITE | \
+                PMD_SECT_AP_READ | \
+                PMD_FLAGS_SMP)
+        ALT_UP(.long \
+                PMD_TYPE_SECT | \
                 PMD_SECT_AP_WRITE | \
                 PMD_SECT_AP_READ | \
-                PMD_FLAGS
+                PMD_FLAGS_UP)
         .long   PMD_TYPE_SECT | \
                 PMD_SECT_XN | \
                 PMD_SECT_AP_WRITE | \