Commit 583248e6620a ("iommu/iova: Disable preemption around use of
this_cpu_ptr()") disables preemption while accessing a per-CPU variable.
This does keep lockdep quiet. However I don't see the point why it is
bad if we get migrated after its access to another CPU.
__iova_rcache_insert() and __iova_rcache_get() immediately locks the
variable after obtaining it - before accessing its members.
_If_ we get migrated away after retrieving the address of cpu_rcache
before taking the lock then the *other* task on the same CPU will
retrieve the same address of cpu_rcache and will spin on the lock.
alloc_iova_fast() disables preemption while invoking
free_cpu_cached_iovas() on each CPU. The function itself uses
per_cpu_ptr() which does not trigger a warning (like this_cpu_ptr()
does). It _could_ make sense to use get_online_cpus() instead but the we
have a hotplug notifier for CPU down (and none for up) so we are good.
Cc: Joerg Roedel <j...@8bytes.org>
Cc: iommu@lists.linux-foundation.org
Cc: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
drivers/iommu/iova.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)
diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index 5c88ba70e4e0..f0ff0aa04081 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -22,6 +22,7 @@
#include <linux/slab.h>
#include <linux/smp.h>
#include <linux/bitops.h>
+#include <linux/cpu.h>
static bool iova_rcache_insert(struct iova_domain *iovad,
unsigned long pfn,
@@ -398,10 +399,8 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long
size,
/* Try replenishing IOVAs by flushing rcache. */
flushed_rcache = true;
- preempt_disable();
for_each_online_cpu(cpu)
free_cpu_cached_iovas(cpu, iovad);
- preempt_enable();
goto retry;
}
@@ -729,7 +728,7 @@ static bool __iova_rcache_insert(struct iova_domain *iovad,
bool can_insert = false;
unsigned long flags;
- cpu_rcache = get_cpu_ptr(rcache->cpu_rcaches);
+ cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches);
spin_lock_irqsave(&cpu_rcache->lock, flags);
if (!iova_magazine_full(cpu_rcache->loaded)) {
@@ -759,7 +758,6 @@ static bool __iova_rcache_insert(struct iova_domain *iovad,
iova_magazine_push(cpu_rcache->loaded, iova_pfn);
spin_unlock_irqrestore(&cpu_rcache->lock, flags);
- put_cpu_ptr(rcache->cpu_rcaches);
if (mag_to_free) {
iova_magazine_free_pfns(mag_to_free, iovad);
@@ -793,7 +791,7 @@ static unsigned long __iova_rcache_get(struct iova_rcache
*rcache,
bool has_pfn = false;
unsigned long flags;
- cpu_rcache = get_cpu_ptr(rcache->cpu_rcaches);
+ cpu_rcache = raw_cpu_ptr(rcache->cpu_rcaches);
spin_lock_irqsave(&cpu_rcache->lock, flags);
if (!iova_magazine_empty(cpu_rcache->loaded)) {
@@ -815,7 +813,6 @@ static unsigned long __iova_rcache_get(struct iova_rcache
*rcache,
iova_pfn = iova_magazine_pop(cpu_rcache->loaded, limit_pfn);
spin_unlock_irqrestore(&cpu_rcache->lock, flags);
- put_cpu_ptr(rcache->cpu_rcaches);
return iova_pfn;
}
--
2.13.1
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