Messages in this thread | | | Subject | Re: [PATCH 1/1] iommu/arm-smmu-v3: fix unexpected CMD_SYNC timeout | From | "Leizhen (ThunderTown)" <> | Date | Thu, 9 Aug 2018 09:30:51 +0800 |
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On 2018/8/8 18:12, Will Deacon wrote: > Hi Thunder, > > On Mon, Aug 06, 2018 at 08:31:29PM +0800, Zhen Lei wrote: >> 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. > > Oh yuck, you're right! We probably want a CC stable on this. Did you see > this go wrong in practice? Just misreported and make the caller wait for a long time until TIMEOUT. It's rare to happen, because any other CMD_SYNC during the waiting period will break it.
> > One comment on your patch... > >> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> >> --- >> drivers/iommu/arm-smmu-v3.c | 7 +++---- >> 1 file changed, 3 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c >> index 1d64710..4810f61 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 */ >> @@ -836,7 +836,6 @@ static int arm_smmu_cmdq_build_cmd(u64 *cmd, struct arm_smmu_cmdq_ent *ent) >> cmd[0] |= FIELD_PREP(CMDQ_SYNC_0_CS, CMDQ_SYNC_0_CS_SEV); >> cmd[0] |= FIELD_PREP(CMDQ_SYNC_0_MSH, ARM_SMMU_SH_ISH); >> cmd[0] |= FIELD_PREP(CMDQ_SYNC_0_MSIATTR, ARM_SMMU_MEMATTR_OIWB); >> - cmd[0] |= FIELD_PREP(CMDQ_SYNC_0_MSIDATA, ent->sync.msidata); >> cmd[1] |= ent->sync.msiaddr & CMDQ_SYNC_1_MSIADDR_MASK; >> break; >> default: >> @@ -947,7 +946,6 @@ 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), >> }, >> }; >> @@ -955,6 +953,8 @@ static int __arm_smmu_cmdq_issue_sync_msi(struct arm_smmu_device *smmu) >> arm_smmu_cmdq_build_cmd(cmd, &ent); >> >> spin_lock_irqsave(&smmu->cmdq.lock, flags); >> + ent.sync.msidata = ++smmu->sync_nr; >> + cmd[0] |= FIELD_PREP(CMDQ_SYNC_0_MSIDATA, ent.sync.msidata); > > I really don't like splitting this out from building the rest of the > command. Can you just move the call to arm_smmu_cmdq_build_cmd into the > critical section, please? OK. I have considered that before, just worry it will increase the compition of spinlock.
In addition, I will append a optimization patch: the adjacent CMD_SYNCs, we only need one.
> > Thanks, > > Will > > . >
-- Thanks! BestRegards
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