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>

1 files changed, 2 insertions, 6 deletions

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index ee9c258d3ae0..0ca985b418ec 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -481,7 +481,7 @@ 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;
@@ -3710,10 +3710,8 @@ static void add_unmap(struct dmar_domain *dom, unsigned long iova_pfn,
         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
@@ -3746,8 +3744,6 @@ static void add_unmap(struct dmar_domain *dom, unsigned long iova_pfn,
         }
         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)