hpsa: DMAR invalid read

[Guilherme G. Piccoli]

Recently in kernel 4.20-rc1 and newer we observed the following spontaneous issue with hpsa when intel_iommu is enabled:

[ 5173.952022] DMAR: DRHD: handling fault status reg 2
[ 5174.190649] DMAR: [DMA Read] Request device [03:00.0] fault addr eefdd000 [fault reason 06] PTE Read access is not set

There's a commit that touches DMA in hpsa: "scsi: hpsa: switch to generic DMA API"
We've tested with this commit reverted on top of 4.20-rc1 and it reproduces (the trigger is a kernel build). We cannot reproduce in 4.19.

Investigation is ongoing.

[Guilherme G. Piccoli (gpiccoli)]

Correction: it happens in 4.19 also. I continue with the bisect process.

[Terry Rudd (terrykrudd)]

Guilherme, is there going to be further work on this bug?

[Guilherme G. Piccoli (gpiccoli)]

Hi Terry, I'm planning to post an update this week.
It seems the problem is related with physical block size adjustments,
after the introduction of the patch: "eb53a3ea3e00 scsi: hpsa: limit transfer length to 1MB, not 512kB"

Without this patch I don't see the issue anymore. But I'm investigating why this patch triggers the issue...

Thanks,

Guilherme

[Guilherme G. Piccoli (gpiccoli)]

I've narrowed down the problem for devices in HBA mode; if device is in RAID mode (despite if it's effectively using some raid level or has only 1 disk), it does not reproduce the issue. I'll attach files with outputs from HP RAID utility (accessed in BIOS) for both cases.
I continue the investigation.

Thanks,

Guilherme

[Guilherme G. Piccoli (gpiccoli)]

The problem was fixed by the following commit, present in all Ubuntu releases: 625d7d351887 ("scsi: hpsa: correct ioaccel2 chaining"). Basically it was an access to a DMA non-mapped region, and was restricted to non-RAID mode adapters due to the I/O path being different.

Since it was fixed, no more work or debug is necessary here.
Cheers,

Guilherme

[Guilherme G. Piccoli (gpiccoli)]

For the current Ubuntu releases, the kernels with this fix are listed below.

* Xenial (16.04)
regular kernel: 4.4.0-159
HWE kernel: 4.15.0-60

* Bionic (18.04)
regular kernel: 4.15.0-60
HWE-Disco kernel: 5.0.0-31

* Disco (19.04)
regular kernel: 5.0.0-31

*Eoan (19.10):
regular kernel: all versions (the upstream fix came in v5.2; Eoan is based on v5.3)