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Date: Mon, 17 Jun 2024 09:18:55 -0700
From: Rob Clark <robdclark@...il.com>
To: Robin Murphy <robin.murphy@....com>
Cc: iommu@...ts.linux.dev, linux-arm-msm@...r.kernel.org,
Stephen Boyd <swboyd@...omium.org>, Rob Clark <robdclark@...omium.org>,
Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>, Jason Gunthorpe <jgg@...pe.ca>,
Jerry Snitselaar <jsnitsel@...hat.com>, Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
"moderated list:ARM SMMU DRIVERS" <linux-arm-kernel@...ts.infradead.org>,
open list <linux-kernel@...r.kernel.org>, Pranjal Shrivastava <praan@...gle.com>
Subject: Re: [PATCH] iommu/arm-smmu: Pretty-print context fault related regs
On Mon, Jun 17, 2024 at 6:07 AM Robin Murphy <robin.murphy@....com> wrote:
>
> On 04/06/2024 4:01 pm, Rob Clark wrote:
> > From: Rob Clark <robdclark@...omium.org>
> >
> > Parse out the bitfields for easier-to-read fault messages.
> >
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> > Stephen was wanting easier to read fault messages.. so I typed this up.
> >
> > Resend with the new iommu list address
> >
> > drivers/iommu/arm/arm-smmu/arm-smmu.c | 53 +++++++++++++++++++++++++--
> > drivers/iommu/arm/arm-smmu/arm-smmu.h | 5 +++
> > 2 files changed, 54 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > index c572d877b0e1..06712d73519c 100644
> > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > @@ -411,6 +411,8 @@ static irqreturn_t arm_smmu_context_fault(int irq, void *dev)
> > unsigned long iova;
> > struct arm_smmu_domain *smmu_domain = dev;
> > struct arm_smmu_device *smmu = smmu_domain->smmu;
> > + static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL,
> > + DEFAULT_RATELIMIT_BURST);
> > int idx = smmu_domain->cfg.cbndx;
> > int ret;
> >
> > @@ -425,10 +427,53 @@ static irqreturn_t arm_smmu_context_fault(int irq, void *dev)
> > ret = report_iommu_fault(&smmu_domain->domain, NULL, 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);
> > + if (ret == -ENOSYS && __ratelimit(&rs)) {
> > + static const struct {
> > + u32 mask; const char *name;
> > + } fsr_bits[] = {
> > + { ARM_SMMU_FSR_MULTI, "MULTI" },
> > + { ARM_SMMU_FSR_SS, "SS" },
> > + { ARM_SMMU_FSR_UUT, "UUT" },
> > + { ARM_SMMU_FSR_ASF, "ASF" },
> > + { ARM_SMMU_FSR_TLBLKF, "TLBLKF" },
> > + { ARM_SMMU_FSR_TLBMCF, "TLBMCF" },
> > + { ARM_SMMU_FSR_EF, "EF" },
> > + { ARM_SMMU_FSR_PF, "PF" },
> > + { ARM_SMMU_FSR_AFF, "AFF" },
> > + { ARM_SMMU_FSR_TF, "TF" },
> > + }, fsynr0_bits[] = {
> > + { ARM_SMMU_FSYNR0_WNR, "WNR" },
> > + { ARM_SMMU_FSYNR0_PNU, "PNU" },
> > + { ARM_SMMU_FSYNR0_IND, "IND" },
> > + { ARM_SMMU_FSYNR0_NSATTR, "NSATTR" },
> > + { ARM_SMMU_FSYNR0_PTWF, "PTWF" },
> > + { ARM_SMMU_FSYNR0_AFR, "AFR" },
> > + };
> > +
> > + pr_err("%s %s: Unhandled context fault: fsr=0x%x (",
> > + dev_driver_string(smmu->dev), dev_name(smmu->dev), fsr);
> > +
> > + for (int i = 0, n = 0; i < ARRAY_SIZE(fsr_bits); i++) {
> > + if (fsr & fsr_bits[i].mask) {
> > + pr_cont("%s%s", (n > 0) ? "|" : "", fsr_bits[i].name);
>
> Given that SMMU faults have a high likelihood of correlating with other
> errors, e.g. the initiating device also reporting that it got an abort
> back, this much pr_cont is a recipe for an unreadable mess. Furthermore,
> just imagine how "helpful" this would be when faults in two contexts are
> reported by two different CPUs at the same time ;)
It looks like arm_smmu_context_fault() is only used with non-threaded
irq's. And this fallback is only used if driver doesn't register it's
own fault handler. So I don't think this will be a problem.
> I'd prefer to retain the original message as-is, so there is at least
> still an unambiguous "atomic" view of a fault's entire state, then
> follow it with a decode more in the style of arm64's ESR logging. TBH I
> also wouldn't disapprove of hiding the additional decode behind a
> command-line/runtime parameter, since a fault storm can cripple a system
> enough as it is, without making the interrupt handler spend even longer
> printing to a potentially slow console.
It _is_ ratelimited. But we could perhaps use a higher loglevel (pr_debug?)
BR,
-R
> > + n++;
> > + }
> > + }
> > +
> > + pr_cont("), iova=0x%08lx, fsynr=0x%x (S1CBNDX=%u", iova, fsynr,
> > + (fsynr >> 16) & 0xff);
>
> Please define all the bitfields properly (and I agree with Pranjal about
> the naming).
>
> Thanks,
> Robin.
>
> > +
> > + for (int i = 0; i < ARRAY_SIZE(fsynr0_bits); i++) {
> > + if (fsynr & fsynr0_bits[i].mask) {
> > + pr_cont("|%s", fsynr0_bits[i].name);
> > + }
> > + }
> > +
> > + pr_cont("|PLVL=%u), cbfrsynra=0x%x, cb=%d\n",
> > + fsynr & 0x3, /* FSYNR0.PLV */
> > + cbfrsynra, idx);
> > +
> > + }
> >
> > arm_smmu_cb_write(smmu, idx, ARM_SMMU_CB_FSR, fsr);
> > return IRQ_HANDLED;
> > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.h b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> > index 836ed6799a80..3b051273718b 100644
> > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.h
> > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.h
> > @@ -223,6 +223,11 @@ enum arm_smmu_cbar_type {
> >
> > #define ARM_SMMU_CB_FSYNR0 0x68
> > #define ARM_SMMU_FSYNR0_WNR BIT(4)
> > +#define ARM_SMMU_FSYNR0_PNU BIT(5)
> > +#define ARM_SMMU_FSYNR0_IND BIT(6)
> > +#define ARM_SMMU_FSYNR0_NSATTR BIT(8)
> > +#define ARM_SMMU_FSYNR0_PTWF BIT(10)
> > +#define ARM_SMMU_FSYNR0_AFR BIT(11)
> >
> > #define ARM_SMMU_CB_FSYNR1 0x6c
> >
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