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SubjectRe: [PATCH v2 1/3] iommu/arm-smmu: Add support for driver IOMMU fault handlers
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 <jcrouse@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? 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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