Commit aaffaa8a authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Joerg Roedel

iommu/iova: Don't disable preempt around this_cpu_ptr()

Commit 583248e6 ("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 <joro@8bytes.org>
Cc: iommu@lists.linux-foundation.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
parent c0bc126f
...@@ -22,6 +22,7 @@ ...@@ -22,6 +22,7 @@
#include <linux/slab.h> #include <linux/slab.h>
#include <linux/smp.h> #include <linux/smp.h>
#include <linux/bitops.h> #include <linux/bitops.h>
#include <linux/cpu.h>
static bool iova_rcache_insert(struct iova_domain *iovad, static bool iova_rcache_insert(struct iova_domain *iovad,
unsigned long pfn, unsigned long pfn,
...@@ -398,10 +399,8 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size, ...@@ -398,10 +399,8 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size,
/* Try replenishing IOVAs by flushing rcache. */ /* Try replenishing IOVAs by flushing rcache. */
flushed_rcache = true; flushed_rcache = true;
preempt_disable();
for_each_online_cpu(cpu) for_each_online_cpu(cpu)
free_cpu_cached_iovas(cpu, iovad); free_cpu_cached_iovas(cpu, iovad);
preempt_enable();
goto retry; goto retry;
} }
...@@ -729,7 +728,7 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, ...@@ -729,7 +728,7 @@ static bool __iova_rcache_insert(struct iova_domain *iovad,
bool can_insert = false; bool can_insert = false;
unsigned long flags; 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); spin_lock_irqsave(&cpu_rcache->lock, flags);
if (!iova_magazine_full(cpu_rcache->loaded)) { if (!iova_magazine_full(cpu_rcache->loaded)) {
...@@ -759,7 +758,6 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, ...@@ -759,7 +758,6 @@ static bool __iova_rcache_insert(struct iova_domain *iovad,
iova_magazine_push(cpu_rcache->loaded, iova_pfn); iova_magazine_push(cpu_rcache->loaded, iova_pfn);
spin_unlock_irqrestore(&cpu_rcache->lock, flags); spin_unlock_irqrestore(&cpu_rcache->lock, flags);
put_cpu_ptr(rcache->cpu_rcaches);
if (mag_to_free) { if (mag_to_free) {
iova_magazine_free_pfns(mag_to_free, iovad); iova_magazine_free_pfns(mag_to_free, iovad);
...@@ -793,7 +791,7 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache, ...@@ -793,7 +791,7 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache,
bool has_pfn = false; bool has_pfn = false;
unsigned long flags; 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); spin_lock_irqsave(&cpu_rcache->lock, flags);
if (!iova_magazine_empty(cpu_rcache->loaded)) { if (!iova_magazine_empty(cpu_rcache->loaded)) {
...@@ -815,7 +813,6 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache, ...@@ -815,7 +813,6 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache,
iova_pfn = iova_magazine_pop(cpu_rcache->loaded, limit_pfn); iova_pfn = iova_magazine_pop(cpu_rcache->loaded, limit_pfn);
spin_unlock_irqrestore(&cpu_rcache->lock, flags); spin_unlock_irqrestore(&cpu_rcache->lock, flags);
put_cpu_ptr(rcache->cpu_rcaches);
return iova_pfn; return iova_pfn;
} }
......
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