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?
One comment on your patch...
> Signed-off-by: Zhen Lei <thunder.leiz...@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?
Thanks,
Will
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
