| From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> |
| Date: Thu, 15 Sep 2016 17:16:44 +0200 |
| Subject: [PATCH] iommu/vt-d: don't disable preemption while accessing |
| deferred_flush() |
| |
| get_cpu() disables preemption and returns the current CPU number. The |
| CPU number is later only used once while retrieving the address of the |
| local's CPU deferred_flush pointer. |
| We can instead use raw_cpu_ptr() while we remain preemptible. The worst |
| thing that can happen is that flush_unmaps_timeout() is invoked multiple |
| times: once by taskA after seeing HIGH_WATER_MARK and then preempted to |
| another CPU and then by taskB which saw HIGH_WATER_MARK on the same CPU |
| as taskA. It is also likely that ->size got from HIGH_WATER_MARK to 0 |
| right after its read because another CPU invoked flush_unmaps_timeout() |
| for this CPU. |
| The access to flush_data is protected by a spinlock so even if we get |
| migrated to another CPU or preempted - the data structure is protected. |
| |
| While at it, I marked deferred_flush static since I can't find a |
| reference to it outside of this file. |
| |
| Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> |
| --- |
| drivers/iommu/intel-iommu.c | 8 ++------ |
| 1 file changed, 2 insertions(+), 6 deletions(-) |
| |
| --- a/drivers/iommu/intel-iommu.c |
| +++ b/drivers/iommu/intel-iommu.c |
| @@ -480,7 +480,7 @@ struct deferred_flush_data { |
| struct deferred_flush_table *tables; |
| }; |
| |
| -DEFINE_PER_CPU(struct deferred_flush_data, deferred_flush); |
| +static DEFINE_PER_CPU(struct deferred_flush_data, deferred_flush); |
| |
| /* bitmap for indexing intel_iommus */ |
| static int g_num_of_iommus; |
| @@ -3720,10 +3720,8 @@ static void add_unmap(struct dmar_domain |
| struct intel_iommu *iommu; |
| struct deferred_flush_entry *entry; |
| struct deferred_flush_data *flush_data; |
| - unsigned int cpuid; |
| |
| - cpuid = get_cpu(); |
| - flush_data = per_cpu_ptr(&deferred_flush, cpuid); |
| + flush_data = raw_cpu_ptr(&deferred_flush); |
| |
| /* Flush all CPUs' entries to avoid deferring too much. If |
| * this becomes a bottleneck, can just flush us, and rely on |
| @@ -3756,8 +3754,6 @@ static void add_unmap(struct dmar_domain |
| } |
| flush_data->size++; |
| spin_unlock_irqrestore(&flush_data->lock, flags); |
| - |
| - put_cpu(); |
| } |
| |
| static void intel_unmap(struct device *dev, dma_addr_t dev_addr, size_t size) |