3.8-stable review patch. If anyone has any objections, please let me know. ------------------ From: Will Deacon <will.deacon@xxxxxxx> commit 8a4e3a9ead7e37ce1505602b564c15da09ac039f upstream. mm->context.id is updated under asid_lock when a new ASID is allocated to an mm_struct. However, it is also read without the lock when a task is being scheduled and checking whether or not the current ASID generation is up-to-date. If two threads of the same process are being scheduled in parallel and the bottom bits of the generation in their mm->context.id match the current generation (that is, the mm_struct has not been used for ~2^24 rollovers) then the non-atomic, lockless access to mm->context.id may yield the incorrect ASID. This patch fixes this issue by making mm->context.id and atomic64_t, ensuring that the generation is always read consistently. For code that only requires access to the ASID bits (e.g. TLB flushing by mm), then the value is accessed directly, which GCC converts to an ldrb. Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx> Signed-off-by: Will Deacon <will.deacon@xxxxxxx> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/arm/include/asm/mmu.h | 8 ++++---- arch/arm/include/asm/mmu_context.h | 2 +- arch/arm/kernel/asm-offsets.c | 2 +- arch/arm/mm/context.c | 21 +++++++++++++-------- 4 files changed, 19 insertions(+), 14 deletions(-) --- a/arch/arm/include/asm/mmu.h +++ b/arch/arm/include/asm/mmu.h @@ -5,15 +5,15 @@ typedef struct { #ifdef CONFIG_CPU_HAS_ASID - u64 id; + atomic64_t id; #endif - unsigned int vmalloc_seq; + unsigned int vmalloc_seq; } mm_context_t; #ifdef CONFIG_CPU_HAS_ASID #define ASID_BITS 8 #define ASID_MASK ((~0ULL) << ASID_BITS) -#define ASID(mm) ((mm)->context.id & ~ASID_MASK) +#define ASID(mm) ((mm)->context.id.counter & ~ASID_MASK) #else #define ASID(mm) (0) #endif @@ -26,7 +26,7 @@ typedef struct { * modified for 2.6 by Hyok S. Choi <hyok.choi@xxxxxxxxxxx> */ typedef struct { - unsigned long end_brk; + unsigned long end_brk; } mm_context_t; #endif --- a/arch/arm/include/asm/mmu_context.h +++ b/arch/arm/include/asm/mmu_context.h @@ -25,7 +25,7 @@ void __check_vmalloc_seq(struct mm_struc #ifdef CONFIG_CPU_HAS_ASID void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk); -#define init_new_context(tsk,mm) ({ mm->context.id = 0; }) +#define init_new_context(tsk,mm) ({ atomic64_set(&mm->context.id, 0); 0; }) #else /* !CONFIG_CPU_HAS_ASID */ --- a/arch/arm/kernel/asm-offsets.c +++ b/arch/arm/kernel/asm-offsets.c @@ -107,7 +107,7 @@ int main(void) BLANK(); #endif #ifdef CONFIG_CPU_HAS_ASID - DEFINE(MM_CONTEXT_ID, offsetof(struct mm_struct, context.id)); + DEFINE(MM_CONTEXT_ID, offsetof(struct mm_struct, context.id.counter)); BLANK(); #endif DEFINE(VMA_VM_MM, offsetof(struct vm_area_struct, vm_mm)); --- a/arch/arm/mm/context.c +++ b/arch/arm/mm/context.c @@ -149,9 +149,9 @@ static int is_reserved_asid(u64 asid) return 0; } -static void new_context(struct mm_struct *mm, unsigned int cpu) +static u64 new_context(struct mm_struct *mm, unsigned int cpu) { - u64 asid = mm->context.id; + u64 asid = atomic64_read(&mm->context.id); u64 generation = atomic64_read(&asid_generation); if (asid != 0 && is_reserved_asid(asid)) { @@ -178,13 +178,14 @@ static void new_context(struct mm_struct cpumask_clear(mm_cpumask(mm)); } - mm->context.id = asid; + return asid; } void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk) { unsigned long flags; unsigned int cpu = smp_processor_id(); + u64 asid; if (unlikely(mm->context.vmalloc_seq != init_mm.context.vmalloc_seq)) __check_vmalloc_seq(mm); @@ -195,19 +196,23 @@ void check_and_switch_context(struct mm_ */ cpu_set_reserved_ttbr0(); - if (!((mm->context.id ^ atomic64_read(&asid_generation)) >> ASID_BITS) - && atomic64_xchg(&per_cpu(active_asids, cpu), mm->context.id)) + asid = atomic64_read(&mm->context.id); + if (!((asid ^ atomic64_read(&asid_generation)) >> ASID_BITS) + && atomic64_xchg(&per_cpu(active_asids, cpu), asid)) goto switch_mm_fastpath; raw_spin_lock_irqsave(&cpu_asid_lock, flags); /* Check that our ASID belongs to the current generation. */ - if ((mm->context.id ^ atomic64_read(&asid_generation)) >> ASID_BITS) - new_context(mm, cpu); + asid = atomic64_read(&mm->context.id); + if ((asid ^ atomic64_read(&asid_generation)) >> ASID_BITS) { + asid = new_context(mm, cpu); + atomic64_set(&mm->context.id, asid); + } if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending)) local_flush_tlb_all(); - atomic64_set(&per_cpu(active_asids, cpu), mm->context.id); + atomic64_set(&per_cpu(active_asids, cpu), asid); cpumask_set_cpu(cpu, mm_cpumask(mm)); raw_spin_unlock_irqrestore(&cpu_asid_lock, flags); -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html