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.
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?
Robin.
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