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 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. Cc: David Woodhouse <dwmw2@infradead.org> Cc: Joerg Roedel <joro@8bytes.org> Cc: iommu@lists.linux-foundation.org Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Joerg Roedel <jroedel@suse.de>
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@ -481,7 +481,7 @@ struct deferred_flush_data {
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struct deferred_flush_table *tables;
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};
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DEFINE_PER_CPU(struct deferred_flush_data, deferred_flush);
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static DEFINE_PER_CPU(struct deferred_flush_data, deferred_flush);
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/* bitmap for indexing intel_iommus */
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static int g_num_of_iommus;
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@ -3710,10 +3710,8 @@ static void add_unmap(struct dmar_domain *dom, unsigned long iova_pfn,
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struct intel_iommu *iommu;
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struct deferred_flush_entry *entry;
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struct deferred_flush_data *flush_data;
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unsigned int cpuid;
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cpuid = get_cpu();
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flush_data = per_cpu_ptr(&deferred_flush, cpuid);
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flush_data = raw_cpu_ptr(&deferred_flush);
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/* Flush all CPUs' entries to avoid deferring too much. If
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* this becomes a bottleneck, can just flush us, and rely on
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@ -3746,8 +3744,6 @@ static void add_unmap(struct dmar_domain *dom, unsigned long iova_pfn,
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}
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flush_data->size++;
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spin_unlock_irqrestore(&flush_data->lock, flags);
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put_cpu();
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}
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static void intel_unmap(struct device *dev, dma_addr_t dev_addr, size_t size)
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