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authorWill Deacon <will.deacon@arm.com>2012-10-19 17:53:01 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2012-10-22 15:33:51 +0100
commit5f40b909728ad784eb43aa309d3c4e9bdf050781 (patch)
treeffe2370e3cdd6a60a24c8e9c53bf5938521ef6da
parent3581fe0ef37ce12ac7a4f74831168352ae848edc (diff)
downloadvexpress-lsk-5f40b909728ad784eb43aa309d3c4e9bdf050781.tar.gz
ARM: 7559/1: smp: switch away from the idmap before updating init_mm.mm_count
When booting a secondary CPU, the primary CPU hands two sets of page tables via the secondary_data struct: (1) swapper_pg_dir: a normal, cacheable, shared (if SMP) mapping of the kernel image (i.e. the tables used by init_mm). (2) idmap_pgd: an uncached mapping of the .idmap.text ELF section. The idmap is generally used when enabling and disabling the MMU, which includes early CPU boot. In this case, the secondary CPU switches to swapper as soon as it enters C code: struct mm_struct *mm = &init_mm; unsigned int cpu = smp_processor_id(); /* * All kernel threads share the same mm context; grab a * reference and switch to it. */ atomic_inc(&mm->mm_count); current->active_mm = mm; cpumask_set_cpu(cpu, mm_cpumask(mm)); cpu_switch_mm(mm->pgd, mm); This causes a problem on ARMv7, where the identity mapping is treated as strongly-ordered leading to architecturally UNPREDICTABLE behaviour of exclusive accesses, such as those used by atomic_inc. This patch re-orders the secondary_start_kernel function so that we switch to swapper before performing any exclusive accesses. Cc: <stable@vger.kernel.org> Cc: David McKay <david.mckay@st.com> Reported-by: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
-rw-r--r--arch/arm/kernel/smp.c14
1 files changed, 10 insertions, 4 deletions
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 8e20754dd31..fbc8b2623d8 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -294,18 +294,24 @@ static void percpu_timer_setup(void);
asmlinkage void __cpuinit secondary_start_kernel(void)
{
struct mm_struct *mm = &init_mm;
- unsigned int cpu = smp_processor_id();
+ unsigned int cpu;
+
+ /*
+ * The identity mapping is uncached (strongly ordered), so
+ * switch away from it before attempting any exclusive accesses.
+ */
+ cpu_switch_mm(mm->pgd, mm);
+ enter_lazy_tlb(mm, current);
+ local_flush_tlb_all();
/*
* All kernel threads share the same mm context; grab a
* reference and switch to it.
*/
+ cpu = smp_processor_id();
atomic_inc(&mm->mm_count);
current->active_mm = mm;
cpumask_set_cpu(cpu, mm_cpumask(mm));
- cpu_switch_mm(mm->pgd, mm);
- enter_lazy_tlb(mm, current);
- local_flush_tlb_all();
printk("CPU%u: Booted secondary processor\n", cpu);