[PATCH] ARM: 2664/2: add support for atomic ops on pre-ARMv6 SMP systems
Patch from Nicolas Pitre
Not that there might be many of them on the planet, but at least RMK
apparently has one.
Signed-off-by: Nicolas Pitre
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 4eb3615..e14278d 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -269,7 +269,7 @@
add r5, sp, #S_PC
ldmia r7, {r2 - r4} @ Get USR pc, cpsr
-#if __LINUX_ARM_ARCH__ < 6
+#if __LINUX_ARM_ARCH__ < 6 && !defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
@ make sure our user space atomic helper is aborted
cmp r2, #VIRT_OFFSET
bichs r3, r3, #PSR_Z_BIT
@@ -616,11 +616,17 @@
__kuser_cmpxchg: @ 0xffff0fc0
-#if __LINUX_ARM_ARCH__ < 6
+#if defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
-#ifdef CONFIG_SMP /* sanity check */
-#error "CONFIG_SMP on a machine supporting pre-ARMv6 processors?"
-#endif
+ /*
+ * Poor you. No fast solution possible...
+ * The kernel itself must perform the operation.
+ * A special ghost syscall is used for that (see traps.c).
+ */
+ swi #0x9ffff0
+ mov pc, lr
+
+#elif __LINUX_ARM_ARCH__ < 6
/*
* Theory of operation:
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 14df16b..45d2a03 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -464,6 +464,55 @@
#endif
return 0;
+#ifdef CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG
+ /*
+ * Atomically store r1 in *r2 if *r2 is equal to r0 for user space.
+ * Return zero in r0 if *MEM was changed or non-zero if no exchange
+ * happened. Also set the user C flag accordingly.
+ * If access permissions have to be fixed up then non-zero is
+ * returned and the operation has to be re-attempted.
+ *
+ * *NOTE*: This is a ghost syscall private to the kernel. Only the
+ * __kuser_cmpxchg code in entry-armv.S should be aware of its
+ * existence. Don't ever use this from user code.
+ */
+ case 0xfff0:
+ {
+ extern void do_DataAbort(unsigned long addr, unsigned int fsr,
+ struct pt_regs *regs);
+ unsigned long val;
+ unsigned long addr = regs->ARM_r2;
+ struct mm_struct *mm = current->mm;
+ pgd_t *pgd; pmd_t *pmd; pte_t *pte;
+
+ regs->ARM_cpsr &= ~PSR_C_BIT;
+ spin_lock(&mm->page_table_lock);
+ pgd = pgd_offset(mm, addr);
+ if (!pgd_present(*pgd))
+ goto bad_access;
+ pmd = pmd_offset(pgd, addr);
+ if (!pmd_present(*pmd))
+ goto bad_access;
+ pte = pte_offset_map(pmd, addr);
+ if (!pte_present(*pte) || !pte_write(*pte))
+ goto bad_access;
+ val = *(unsigned long *)addr;
+ val -= regs->ARM_r0;
+ if (val == 0) {
+ *(unsigned long *)addr = regs->ARM_r1;
+ regs->ARM_cpsr |= PSR_C_BIT;
+ }
+ spin_unlock(&mm->page_table_lock);
+ return val;
+
+ bad_access:
+ spin_unlock(&mm->page_table_lock);
+ /* simulate a read access fault */
+ do_DataAbort(addr, 15 + (1 << 11), regs);
+ return -1;
+ }
+#endif
+
default:
/* Calls 9f00xx..9f07ff are defined to return -ENOSYS
if not implemented, rather than raising SIGILL. This
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index ade0e22..3fefb43 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -422,3 +422,11 @@
assume directly accessing that register and always obtain the
expected value only on ARMv7 and above.
+config NEEDS_SYSCALL_FOR_CMPXCHG
+ bool
+ default y if SMP && (CPU_32v5 || CPU_32v4 || CPU_32v3)
+ help
+ SMP on a pre-ARMv6 processor? Well OK then.
+ Forget about fast user space cmpxchg support.
+ It is just not possible.
+
