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>
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 6e8f05c..062b58c 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -154,16 +154,39 @@
.long 9999b,9001f; \
.popsection
+#ifdef CONFIG_SMP
+#define ALT_SMP(instr...) \
+9998: instr
+#define ALT_UP(instr...) \
+ .pushsection ".alt.smp.init", "a" ;\
+ .long 9998b ;\
+ instr ;\
+ .popsection
+#define ALT_UP_B(label) \
+ .equ up_b_offset, label - 9998b ;\
+ .pushsection ".alt.smp.init", "a" ;\
+ .long 9998b ;\
+ b . + up_b_offset ;\
+ .popsection
+#else
+#define ALT_SMP(instr...)
+#define ALT_UP(instr...) instr
+#define ALT_UP_B(label) b label
+#endif
+
/*
* SMP data memory barrier
*/
.macro smp_dmb
#ifdef CONFIG_SMP
#if __LINUX_ARM_ARCH__ >= 7
- dmb
+ ALT_SMP(dmb)
#elif __LINUX_ARM_ARCH__ == 6
- mcr p15, 0, r0, c7, c10, 5 @ dmb
+ ALT_SMP(mcr p15, 0, r0, c7, c10, 5) @ dmb
+#else
+#error Incompatible SMP platform
#endif
+ ALT_UP(nop)
#endif
.endm
diff --git a/arch/arm/include/asm/smp_mpidr.h b/arch/arm/include/asm/smp_mpidr.h
index 7da7105..6a9307d 100644
--- a/arch/arm/include/asm/smp_mpidr.h
+++ b/arch/arm/include/asm/smp_mpidr.h
@@ -4,7 +4,12 @@
#define hard_smp_processor_id() \
({ \
unsigned int cpunum; \
- __asm__("mrc p15, 0, %0, c0, c0, 5\n" \
+ __asm__("\n" \
+ "1: mrc p15, 0, %0, c0, c0, 5\n" \
+ " .pushsection \".alt.smp.init\", \"a\"\n"\
+ " .long 1b\n" \
+ " mov %0, #0\n" \
+ " .popsection" \
: "=r" (cpunum)); \
cpunum &= 0x0F; \
})
diff --git a/arch/arm/include/asm/smp_plat.h b/arch/arm/include/asm/smp_plat.h
index e621530..7de5aa5 100644
--- a/arch/arm/include/asm/smp_plat.h
+++ b/arch/arm/include/asm/smp_plat.h
@@ -18,4 +18,19 @@
return ((read_cpuid_ext(CPUID_EXT_MMFR3) >> 12) & 0xf) < 1;
}
+/*
+ * Return true if we are running on a SMP platform
+ */
+static inline bool is_smp(void)
+{
+#ifndef CONFIG_SMP
+ return false;
+#elif defined(CONFIG_SMP_ON_UP)
+ extern unsigned int smp_on_up;
+ return !!smp_on_up;
+#else
+ return true;
+#endif
+}
+
#endif
diff --git a/arch/arm/include/asm/tlbflush.h b/arch/arm/include/asm/tlbflush.h
index 33b546a..cf2f018 100644
--- a/arch/arm/include/asm/tlbflush.h
+++ b/arch/arm/include/asm/tlbflush.h
@@ -70,6 +70,10 @@
#undef _TLB
#undef MULTI_TLB
+#ifdef CONFIG_SMP_ON_UP
+#define MULTI_TLB 1
+#endif
+
#define v3_tlb_flags (TLB_V3_FULL | TLB_V3_PAGE)
#ifdef CONFIG_CPU_TLB_V3
@@ -185,17 +189,23 @@
# define v6wbi_always_flags (-1UL)
#endif
-#ifdef CONFIG_SMP
-#define v7wbi_tlb_flags (TLB_WB | TLB_DCLEAN | TLB_V7_IS_BTB | \
+#define v7wbi_tlb_flags_smp (TLB_WB | TLB_DCLEAN | TLB_V7_IS_BTB | \
TLB_V7_UIS_FULL | TLB_V7_UIS_PAGE | TLB_V7_UIS_ASID)
-#else
-#define v7wbi_tlb_flags (TLB_WB | TLB_DCLEAN | TLB_BTB | \
+#define v7wbi_tlb_flags_up (TLB_WB | TLB_DCLEAN | TLB_BTB | \
TLB_V6_U_FULL | TLB_V6_U_PAGE | TLB_V6_U_ASID)
-#endif
#ifdef CONFIG_CPU_TLB_V7
-# define v7wbi_possible_flags v7wbi_tlb_flags
-# define v7wbi_always_flags v7wbi_tlb_flags
+
+# ifdef CONFIG_SMP_ON_UP
+# define v7wbi_possible_flags (v7wbi_tlb_flags_smp | v7wbi_tlb_flags_up)
+# define v7wbi_always_flags (v7wbi_tlb_flags_smp & v7wbi_tlb_flags_up)
+# elif defined(CONFIG_SMP)
+# define v7wbi_possible_flags v7wbi_tlb_flags_smp
+# define v7wbi_always_flags v7wbi_tlb_flags_smp
+# else
+# define v7wbi_possible_flags v7wbi_tlb_flags_up
+# define v7wbi_always_flags v7wbi_tlb_flags_up
+# endif
# ifdef _TLB
# define MULTI_TLB 1
# else