From: Zhen Lei <thunder.leizhen@huawei.com>
To: Robin Murphy <robin.murphy@arm.com>,
Will Deacon <will.deacon@arm.com>, Joerg Roedel <joro@8bytes.org>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
iommu <iommu@lists.linux-foundation.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Cc: Zhen Lei <thunder.leizhen@huawei.com>,
LinuxArm <linuxarm@huawei.com>, Hanjun Guo <guohanjun@huawei.com>,
Libin <huawei.libin@huawei.com>
Subject: [PATCH v2 1/2] iommu/arm-smmu-v3: fix unexpected CMD_SYNC timeout
Date: Thu, 9 Aug 2018 19:48:52 +0800 [thread overview]
Message-ID: <1533815333-17320-2-git-send-email-thunder.leizhen@huawei.com> (raw)
In-Reply-To: <1533815333-17320-1-git-send-email-thunder.leizhen@huawei.com>
The condition "(int)(VAL - sync_idx) >= 0" to break loop in function
__arm_smmu_sync_poll_msi requires that sync_idx must be increased
monotonously according to the sequence of the CMDs in the cmdq.
But ".msidata = atomic_inc_return_relaxed(&smmu->sync_nr)" is not protected
by spinlock, so the following scenarios may appear:
cpu0 cpu1
msidata=0
msidata=1
insert cmd1
insert cmd0
smmu execute cmd1
smmu execute cmd0
poll timeout, because msidata=1 is overridden by
cmd0, that means VAL=0, sync_idx=1.
This is not a functional problem, just make the caller wait for a long
time until TIMEOUT. It's rare to happen, because any other CMD_SYNCs
during the waiting period will break it.
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
drivers/iommu/arm-smmu-v3.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 1d64710..d17a9a7 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -566,7 +566,7 @@ struct arm_smmu_device {
int gerr_irq;
int combined_irq;
- atomic_t sync_nr;
+ u32 sync_nr;
unsigned long ias; /* IPA */
unsigned long oas; /* PA */
@@ -947,14 +947,13 @@ static int __arm_smmu_cmdq_issue_sync_msi(struct arm_smmu_device *smmu)
struct arm_smmu_cmdq_ent ent = {
.opcode = CMDQ_OP_CMD_SYNC,
.sync = {
- .msidata = atomic_inc_return_relaxed(&smmu->sync_nr),
.msiaddr = virt_to_phys(&smmu->sync_count),
},
};
- arm_smmu_cmdq_build_cmd(cmd, &ent);
-
spin_lock_irqsave(&smmu->cmdq.lock, flags);
+ ent.sync.msidata = ++smmu->sync_nr;
+ arm_smmu_cmdq_build_cmd(cmd, &ent);
arm_smmu_cmdq_insert_cmd(smmu, cmd);
spin_unlock_irqrestore(&smmu->cmdq.lock, flags);
@@ -2179,7 +2178,6 @@ static int arm_smmu_init_structures(struct arm_smmu_device *smmu)
{
int ret;
- atomic_set(&smmu->sync_nr, 0);
ret = arm_smmu_init_queues(smmu);
if (ret)
return ret;
--
1.8.3
next prev parent reply other threads:[~2018-08-09 11:50 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-09 11:48 [PATCH v2 0/2] bugfix and optimization about CMD_SYNC Zhen Lei
2018-08-09 11:48 ` Zhen Lei [this message]
2018-08-09 11:48 ` [PATCH v2 2/2] iommu/arm-smmu-v3: avoid redundant CMD_SYNCs if possible Zhen Lei
2018-08-09 12:02 ` Robin Murphy
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