[PATCH] iommu/arm-smmu-v3: Add rmb after reading event queue prod_reg

[PATCH] iommu/arm-smmu-v3: Add rmb after reading event queue prod_reg

[Zhou Wang]

In arm_smmu_evtq_thread, reading event queue is from consumer pointer,
which has no address dependency on producer pointer, prog_reg(MMIO) and
event queue memory(Normal memory) can disorder. So the load for event queue
can be done before the load of prod_reg, then perhaps wrong event entry
value will be got.

Add rmb to make sure to get correct event queue entry value.

Signed-off-by: Zhou Wang <wangzhou1@hisilicon.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index c192544..93c9077 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -819,6 +819,9 @@ static int queue_sync_prod_in(struct arm_smmu_queue *q)
 	int ret = 0;
 	u32 prod = readl_relaxed(q->prod_reg);
 
+	/* Ensure that reading event queue is after reading prod_reg */
+	rmb();
+
 	if (Q_OVF(prod) != Q_OVF(q->llq.prod))
 		ret = -EOVERFLOW;
 
-- 
2.8.1

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Re: [PATCH] iommu/arm-smmu-v3: Add rmb after reading event queue prod_reg

[Will Deacon]

On Mon, 28 Sep 2020 16:32:02 +0800, Zhou Wang wrote:
> In arm_smmu_evtq_thread, reading event queue is from consumer pointer,
> which has no address dependency on producer pointer, prog_reg(MMIO) and
> event queue memory(Normal memory) can disorder. So the load for event queue
> can be done before the load of prod_reg, then perhaps wrong event entry
> value will be got.
> 
> Add rmb to make sure to get correct event queue entry value.

Applied to will (for-joerg/arm-smmu/updates), thanks!

[1/1] iommu/arm-smmu-v3: Add rmb after reading event queue prod_reg
      https://git.kernel.org/will/c/a76a37777f2c 

(please note that I changed the patch to use readl() instead of an rmb()
in conjunction with the _relaxed() accessor, and then adjusted the cons
side to match in terms of DMB vs DSB).

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev
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Re: [PATCH] iommu/arm-smmu-v3: Add rmb after reading event queue prod_reg

[Zhou Wang]

On 2020/9/29 6:13, Will Deacon wrote:
> On Mon, 28 Sep 2020 16:32:02 +0800, Zhou Wang wrote:
>> In arm_smmu_evtq_thread, reading event queue is from consumer pointer,
>> which has no address dependency on producer pointer, prog_reg(MMIO) and
>> event queue memory(Normal memory) can disorder. So the load for event queue
>> can be done before the load of prod_reg, then perhaps wrong event entry
>> value will be got.
>>
>> Add rmb to make sure to get correct event queue entry value.
> 
> Applied to will (for-joerg/arm-smmu/updates), thanks!
> 
> [1/1] iommu/arm-smmu-v3: Add rmb after reading event queue prod_reg
>       https://git.kernel.org/will/c/a76a37777f2c 
> 
> (please note that I changed the patch to use readl() instead of an rmb()
> in conjunction with the _relaxed() accessor, and then adjusted the cons
> side to match in terms of DMB vs DSB).

Thanks for taking this patch!

Best,
Zhou

> 
> Cheers,
> 
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