48 lines
1.7 KiB
Diff
48 lines
1.7 KiB
Diff
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From 7815b06b01c933130d61902d388f4dd15c9849fd Mon Sep 17 00:00:00 2001
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Thu, 15 Sep 2016 16:58:19 +0200
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Subject: [PATCH 037/365] iommu/iova: don't disable preempt around
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this_cpu_ptr()
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X-NVConfidentiality: public
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Commit 583248e6620a ("iommu/iova: Disable preemption around use of
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this_cpu_ptr()") disables preemption while accessing a per-CPU variable.
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This does keep lockdep quiet. However I don't see the point why it is
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bad if we get migrated after its access to another CPU.
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__iova_rcache_insert() and __iova_rcache_get() immediately locks the
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variable after obtaining it - before accessing its members.
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_If_ we get migrated away after retrieving the address of cpu_rcache
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before taking the lock then the *other* task on the same CPU will
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retrieve the same address of cpu_rcache and will spin on the lock.
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alloc_iova_fast() disables preemption while invoking
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free_cpu_cached_iovas() on each CPU. The function itself uses
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per_cpu_ptr() which does not trigger a warning (like this_cpu_ptr()
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does) because it assumes the caller knows what he does because he might
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access the data structure from a different CPU (which means he needs
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protection against concurrent access).
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Change-Id: Icaa40e90958ac7ff6c29c21017560000e303b992
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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drivers/iommu/iova.c | 1 +
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1 file changed, 1 insertion(+)
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diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
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index 1abdd11..3ee073b 100644
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--- a/drivers/iommu/iova.c
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+++ b/drivers/iommu/iova.c
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@@ -24,6 +24,7 @@
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#include <linux/bitops.h>
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#include <linux/cpu.h>
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+
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static bool iova_rcache_insert(struct iova_domain *iovad,
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unsigned long pfn,
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unsigned long size);
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--
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2.7.4
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