On Mon, Mar 23, 2020 at 10:28 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
>
> On 2020-03-23 3:21 pm, Prabhakar Kushwaha wrote:
> > Hi All,
> >
> > I am facing issue on Marvell's ARM64 Thunder X2 with kdump kernel.
> > Here network card is continuously giving following AER error
> > [ 100.839168] igb 0000:09:00.1: AER: aer_status: 0x00004000,
> > aer_mask: 0x00000000
> > [ 100.846463] igb 0000:09:00.1: AER: [14] CmpltTO (First)
> > [ 100.861491] igb 0000:09:00.1: AER: aer_layer=Transaction Layer,
> > aer_agent=Requester ID
> > [ 100.869400] igb 0000:09:00.1: AER: aer_uncor_severity: 0x00062011
> >
> > This error is not 100% reproducible. It happens 1 out of 4 try.
> >
> > This error goes away in following two scenarios
> > A) Set iommu in bypass mode via bootargs iommu.passthrough=1
> > B) Wait for ~100ms in arm_smmu_device_reset of drivers/iommu/arm-smmu-v3.c
> > if (reg & CR0_SMMUEN) {
> > dev_warn(smmu->dev, "SMMU currently enabled! Resetting...\n");
> > WARN_ON(is_kdump_kernel() && !disable_bypass);
> > mdelay(100); <-- Added delay
> > arm_smmu_update_gbpa(smmu, GBPA_ABORT, 0);
> > }
> >
> > From A), it is clear that it is related to IOMMU
> > From B), looks like during boot of kdump kernel, network card is still
> > active and it has sent some request over PCIe.
> > as GPBA_ABORT bit is set, no response/completion coming to PCIe
> > controller hence "CmpltTO" error.
> >
> > Ideally before setting GPBA_ABORT bit, there should be some check for
> > active transaction. if it is not possible, a wait should be done to
> > assure that no more pending transaction left.
>
> In general there is no way to check for active transactions, and even if
> there were, waiting for them to finish could mean waiting forever (if,
> say, a device is continuously streaming to/from a ring buffer).
>
> > why any such delay has not been considered?
>
> The main aim here is to block any DMA left over from the crashed kernel
> as quickly as possible, to minimise any further potential corruption of
> memory (consider if a device was left writing to an IOMMU virtual
> address that happened to have the same value as some physical address in
> the crash kernel's reserved memory). The fact that an arbitrary delay
> happens to give a 'nicer' result in one particular situation on one
> particular platform is neither here nor there in general.
>
I agree.
But we are depending upon kdump boot time and expecting devices to
reach to idle state before setting GBPA_ABORT bit.
adding a delay will be fair and make it independent of kdump boot time.
> Besides, this is *crash* kernel, so yeah, expect errors - something's
> already gone badly wrong to get us here, and everything from then on is
> merely a best-effort attempt to salvage what we can. Does it even make
> sense to have AER enabled at this point?
>
i tried by disabling AER in kdump kernel. but it did not helped as
network device become out of sync with respect to tx unit causing it
to be hanged and it never recovered from there. Same can happen with
other devices like SATA etc
--pk
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