Re: [PATCH v3 1/2] iommu/arm-smmu-v3: fix unexpected CMD_SYNC timeout

From: Robin Murphy
Date: Thu Aug 16 2018 - 05:27:48 EST

On 2018-08-16 10:18 AM, Will Deacon wrote:
On Thu, Aug 16, 2018 at 04:21:17PM +0800, Leizhen (ThunderTown) wrote:
On 2018/8/15 20:26, Robin Murphy wrote:
On 15/08/18 11:23, Zhen Lei wrote:
diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 1d64710..3f5c236 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 */
@@ -775,6 +775,11 @@ static int queue_remove_raw(struct arm_smmu_queue *q, u64 *ent)
return 0;

+static inline void arm_smmu_cmdq_sync_set_msidata(u64 *cmd, u32 msidata)

If we *are* going to go down this route then I think it would make sense
to move the msiaddr and CMDQ_SYNC_0_CS_MSI logic here as well; i.e.
arm_smmu_cmdq_build_cmd() always generates a "normal" SEV-based sync
command, then calling this guy would convert it to an MSI-based one.
As-is, having bits of mutually-dependent data handled across two
separate places just seems too messy and error-prone.

Yes, How about create a new function "arm_smmu_cmdq_build_sync_msi_cmd"?

static inline
void arm_smmu_cmdq_build_sync_msi_cmd(u64 *cmd, struct arm_smmu_cmdq_ent *ent)
cmd[0] = FIELD_PREP(CMDQ_0_OP, ent->opcode);
cmd[1] = ent->sync.msiaddr & CMDQ_SYNC_1_MSIADDR_MASK;

None of this seems justified given the numbers from John, so please just do
the simple thing and build the command with the lock held.

Agreed - sorry if my wording was unclear, but that suggestion was only for the possibility of it proving genuinely worthwhile to build the command outside the lock. Since that isn't the case, I definitely prefer the simpler approach too.