iommu/arm-smmu-v3: Fix unexpected CMD_SYNC timeout

The condition break condition of:

	(int)(VAL - sync_idx) >= 0

in the __arm_smmu_sync_poll_msi() polling loop requires that sync_idx
must be increased monotonically according to the sequence of the CMDs in
the cmdq.

However, since the msidata is populated using atomic_inc_return_relaxed()
before taking the command-queue spinlock, then the following scenario
can occur:

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, since the caller will eventually either
timeout or exit due to another CMD_SYNC, however it's clearly not what
the code is supposed to be doing. Fix it, by incrementing the sequence
count with the command-queue lock held, allowing us to drop the atomic
operations altogether.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[will: dropped the specialised cmd building routine for now]
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index feef1226f70522ac98ea218677b5777224c5e122..48baffd07aef3cdee09a8e2688af384064f82d45 100644 (file)
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -567,7 +567,7 @@ 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 */
@@ -948,14 +948,13 @@ 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);
 
@@ -2180,7 +2179,6 @@ 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;