Re: [PATCH v2 1/3] iommu/arm-smmu: Add support for driver IOMMU fault handlers

[Robin Murphy]

On 2021-01-22 12:41, Will Deacon wrote:
On Tue, Nov 24, 2020 at 12:15:58PM -0700, Jordan Crouse wrote:
Call report_iommu_fault() to allow upper-level drivers to register their
own fault handlers.
Signed-off-by: Jordan Crouse <jcro...@codeaurora.org>
---

  drivers/iommu/arm/arm-smmu/arm-smmu.c | 16 +++++++++++++---
  1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c 
b/drivers/iommu/arm/arm-smmu/arm-smmu.c
index 0f28a8614da3..7fd18bbda8f5 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
@@ -427,6 +427,7 @@ static irqreturn_t arm_smmu_context_fault(int irq, void 
*dev)
        struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
        struct arm_smmu_device *smmu = smmu_domain->smmu;
        int idx = smmu_domain->cfg.cbndx;
+       int ret;
  
  	fsr = arm_smmu_cb_read(smmu, idx, ARM_SMMU_CB_FSR);
        if (!(fsr & ARM_SMMU_FSR_FAULT))
@@ -436,11 +437,20 @@ static irqreturn_t arm_smmu_context_fault(int irq, void 
*dev)
        iova = arm_smmu_cb_readq(smmu, idx, ARM_SMMU_CB_FAR);
        cbfrsynra = arm_smmu_gr1_read(smmu, ARM_SMMU_GR1_CBFRSYNRA(idx));
  
-	dev_err_ratelimited(smmu->dev,
-       "Unhandled context fault: fsr=0x%x, iova=0x%08lx, fsynr=0x%x, 
cbfrsynra=0x%x, cb=%d\n",
+       ret = report_iommu_fault(domain, dev, iova,
+               fsynr & ARM_SMMU_FSYNR0_WNR ? IOMMU_FAULT_WRITE : 
IOMMU_FAULT_READ);
+
+       if (ret == -ENOSYS)
+               dev_err_ratelimited(smmu->dev,
+               "Unhandled context fault: fsr=0x%x, iova=0x%08lx, fsynr=0x%x, 
cbfrsynra=0x%x, cb=%d\n",
                            fsr, iova, fsynr, cbfrsynra, idx);
  
-	arm_smmu_cb_write(smmu, idx, ARM_SMMU_CB_FSR, fsr);
+       /*
+        * If the iommu fault returns an error (except -ENOSYS) then assume that
+        * they will handle resuming on their own
+        */
+       if (!ret || ret == -ENOSYS)
+               arm_smmu_cb_write(smmu, idx, ARM_SMMU_CB_FSR, fsr);

Hmm, I don't grok this part. If the fault handler returned an error and
we don't clear the FSR, won't we just re-take the irq immediately?

If we don't touch the FSR at all, yes. Even if we clear the fault 
indicator bits, the interrupt *might* remain asserted until a stalled 
transaction is actually resolved - that's that lovely IMP-DEF corner.

Robin.

I think
it would be better to do this unconditionally, and print the "Unhandled
context fault" message for any non-zero value of ret.

Will

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