Re: Error reports at boot time in Ampere Altra machines since c733ebb7c

[Marc Zyngier <maz@kernel.org>]

On Fri, 03 Mar 2023 19:38:40 +0000,
Darren Hart <darren@os.amperecomputing.com> wrote:
> 
> On Thu, Mar 02, 2023 at 11:25:37PM +0000, Marc Zyngier wrote:
> > On Thu, 02 Mar 2023 20:17:32 +0000,
> > Aristeu Rozanski <aris@redhat.com> wrote:
> > > 
> > > Hi Marc,
> > > 
> > > Since c733ebb7cb67d ("irqchip/gic-v3-its: Reset each ITS's BASERn
> > > register before probe"), Ampere Altra machines are reporting corrected
> > > errors during boot:
> > > 
> > > 	[    0.294334] HEST: Table parsing has been initialized.
> > > 	[    0.294397] sdei: SDEIv1.0 (0x0) detected in firmware.
> > > 	[    0.299622] {1}[Hardware Error]: Hardware error from APEI Generic Hardware Error Source: 0
> > > 	[    0.299626] {1}[Hardware Error]: event severity: recoverable
> > > 	[    0.299629] {1}[Hardware Error]:  Error 0, type: recoverable
> > > 	[    0.299633] {1}[Hardware Error]:   section type: unknown, e8ed898d-df16-43cc-8ecc-54f060ef157f
> > > 	[    0.299638] {1}[Hardware Error]:   section length: 0x30
> > > 	[    0.299645] {1}[Hardware Error]:   00000000: 00000005 ec30000e 00080110 80001001  ......0.........
> > > 	[    0.299648] {1}[Hardware Error]:   00000010: 00000300 00000000 00000000 00000000  ................
> > > 	[    0.299650] {1}[Hardware Error]:   00000020: 00000000 00000000 00000000 00000000  ................
> > > 	[    0.299714] {2}[Hardware Error]: Hardware error from APEI Generic Hardware Error Source: 3
> > > 	[    0.299716] {2}[Hardware Error]: event severity: recoverable
> > > 	[    0.299717] {2}[Hardware Error]:  Error 0, type: recoverable
> > > 	[    0.299718] {2}[Hardware Error]:   section type: unknown, e8ed898d-df16-43cc-8ecc-54f060ef157f
> > > 	[    0.299720] {2}[Hardware Error]:   section length: 0x30
> > > 	[    0.299722] {2}[Hardware Error]:   00000000: 40000005 ec30000e 00080110 80005001  ...@..0......P..
> > > 	[    0.299724] {2}[Hardware Error]:   00000010: 00000300 00000000 00000000 00000000  ................
> > > 	[    0.299726] {2}[Hardware Error]:   00000020: 00000000 00000000 00000000 00000000  ................
> > > 	[    0.299912] GHES: APEI firmware first mode is enabled by APEI bit.
> > > 
> > > Because the errors are being reported later in boot, it's hard to
> > > pinpoint exactly what's causing it without decoding the error information,
> > > which I currently don't know how to do it.
> > 
> > + Darren
> > 
> > Hopefully someone at Ampere can decode this and tell us what is happening.
> 
> Hi Marc,
> 
> + D Scott
> 
> Thanks for the connection.
> 
> This is reporting that something attempted to access GITS2_BASER2, the base
> register for the gicv4 vcpu table. Altra doesn't support gicv4. Is c733ebb7c
> assuming GITS_BASER2 should be accessible on gicv3?

All the GITS_BASERn registers should be RES0 if not implemented, as
per the spec (12.19.1 GITS_BASER<n>, ITS Translation Table
Descriptors, n = 0 - 7)

<quote>
A maximum of 8 GITS_BASER<n> registers can be provided. Unimplemented
registers are RES 0.
</quote>

Returning an error on access is thus definitely a violation of the
spec.

So either the GIC implementation you are using is buggy, or you have
some sort of HW firewalling between the CPU and the GIC that is
trigger happy. My hunch is that this is the latter, as buggy
implementations tend to return an SError when missing this sort of
detail.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.