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Message-ID: <CAF6AEGuDq=YcyKuTfr1xZtff+VGyeeVWe40E4KEy--umwepcEQ@mail.gmail.com>
Date: Tue, 18 Jun 2024 07:57:51 -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 10:33 AM Robin Murphy <robin.murphy@....com> wrote:
>
> On 2024-06-17 5:18 pm, Rob Clark wrote:
> > 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.
>
> You don't think two different IRQs can fire on two different CPUs at the
> same time (or close to)? It's already bad enough when multiple CPUs
> panic and one has to pick apart line-by-line interleaving of the
> registers/stacktraces - imagine how much more utterly unusable that
> would be with bits of different dumps randomly pr_cont'ed together onto
> the same line(s)...
_different_ irq's, yes
Anyways, the reason for pr_cont() was that there wasn't another
reasonable way to decide where separator chars were needed with a
single pr_err(). I could instead construct a string on stack and
print that in a single call, but pr_cont() seemed like the more
reasonable alternative.
BR,
-R
> Even when unrelated stuff gets interleaved because other CPUs just
> happen to be calling printk() at the same time for unrelated reasons
> it's still annoying, and pr_cont makes a bigger mess than not.
> >> 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?)
>
> Yeah, I'd have no complaint with pr_debug/dev_dbg either, if that suits
> your use case. True that the ratelimit may typically mitigate the
> overall impact, but still in the worst case with a sufficiently slow
> console and/or a sufficiently large amount to print per __ratelimit()
> call, it can end up being slow enough to stay below the threshold. Don't
> ask me how I know that :)
>
> Thanks,
> Robin.
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