From: Joakim Tjernlund <Joakim.Tjernlund@infinera•com>
To: "linuxppc-dev@lists•ozlabs.org" <linuxppc-dev@lists•ozlabs.org>,
"leoyang.li@nxp•com" <leoyang.li@nxp•com>,
"york.sun@nxp•com" <york.sun@nxp•com>
Subject: Re: Machine Check in P2010(e500v2)
Date: Sat, 9 Sep 2017 12:45:43 +0000 [thread overview]
Message-ID: <1504961140.31322.69.camel@infinera.com> (raw)
In-Reply-To: <AM4PR0401MB1699D52CA4E6FB227412D9608F950@AM4PR0401MB1699.eurprd04.prod.outlook.com>
On Fri, 2017-09-08 at 22:27 +0000, Leo Li wrote:
> > -----Original Message-----
> > From: Joakim Tjernlund [mailto:Joakim.Tjernlund@infinera•com]
> > Sent: Friday, September 08, 2017 7:51 AM
> > To: linuxppc-dev@lists•ozlabs.org; Leo Li <leoyang.li@nxp•com>; York Su=
n
> > <york.sun@nxp•com>
> > Subject: Re: Machine Check in P2010(e500v2)
> >=20
> > On Fri, 2017-09-08 at 11:54 +0200, Joakim Tjernlund wrote:
> > > On Thu, 2017-09-07 at 18:54 +0000, Leo Li wrote:
> > > > > -----Original Message-----
> > > > > From: Joakim Tjernlund [mailto:Joakim.Tjernlund@infinera•com]
> > > > > Sent: Thursday, September 07, 2017 3:41 AM
> > > > > To: linuxppc-dev@lists•ozlabs.org; Leo Li <leoyang.li@nxp•com>;
> > > > > York Sun <york.sun@nxp•com>
> > > > > Subject: Re: Machine Check in P2010(e500v2)
> > > > >=20
> > > > > On Thu, 2017-09-07 at 00:50 +0200, Joakim Tjernlund wrote:
> > > > > > On Wed, 2017-09-06 at 21:13 +0000, Leo Li wrote:
> > > > > > > > -----Original Message-----
> > > > > > > > From: Joakim Tjernlund
> > > > > > > > [mailto:Joakim.Tjernlund@infinera•com]
> > > > > > > > Sent: Wednesday, September 06, 2017 3:54 PM
> > > > > > > > To: linuxppc-dev@lists•ozlabs.org; Leo Li
> > > > > > > > <leoyang.li@nxp•com>; York Sun <york.sun@nxp•com>
> > > > > > > > Subject: Re: Machine Check in P2010(e500v2)
> > > > > > > >=20
> > > > > > > > On Wed, 2017-09-06 at 20:28 +0000, Leo Li wrote:
> > > > > > > > > > -----Original Message-----
> > > > > > > > > > From: Joakim Tjernlund
> > > > > > > > > > [mailto:Joakim.Tjernlund@infinera•com]
> > > > > > > > > > Sent: Wednesday, September 06, 2017 3:17 PM
> > > > > > > > > > To: linuxppc-dev@lists•ozlabs.org; Leo Li
> > > > > > > > > > <leoyang.li@nxp•com>; York Sun <york.sun@nxp•com>
> > > > > > > > > > Subject: Re: Machine Check in P2010(e500v2)
> > > > > > > > > >=20
> > > > > > > > > > On Wed, 2017-09-06 at 19:31 +0000, Leo Li wrote:
> > > > > > > > > > > > -----Original Message-----
> > > > > > > > > > > > From: York Sun
> > > > > > > > > > > > Sent: Wednesday, September 06, 2017 10:38 AM
> > > > > > > > > > > > To: Joakim Tjernlund
> > > > > > > > > > > > <Joakim.Tjernlund@infinera•com>;
> > > > > > > > > > > > linuxppc- dev@lists•ozlabs.org; Leo Li
> > > > > > > > > > > > <leoyang.li@nxp•com>
> > > > > > > > > > > > Subject: Re: Machine Check in P2010(e500v2)
> > > > > > > > > > > >=20
> > > > > > > > > > > > Scott is no longer with Freescale/NXP. Adding Leo.
> > > > > > > > > > > >=20
> > > > > > > > > > > > On 09/05/2017 01:40 AM, Joakim Tjernlund wrote:
> > > > > > > > > > > > > So after some debugging I found this bug:
> > > > > > > > > > > > > @@ -996,7 +998,7 @@ int
> > > > > > > > > > > > > fsl_pci_mcheck_exception(struct pt_regs
> > > > > > > >=20
> > > > > > > > *regs)
> > > > > > > > > > > > > if (is_in_pci_mem_space(addr)) {
> > > > > > > > > > > > > if (user_mode(regs)) {
> > > > > > > > > > > > > pagefault_disable();
> > > > > > > > > > > > > - ret =3D get_user(regs->ni=
p, &inst);
> > > > > > > > > > > > > + ret =3D get_user(inst,
> > > > > > > > > > > > > + (__u32 __user *)regs->nip);
> > > > > > > > > > > > > pagefault_enable();
> > > > > > > > > > > > > } else {
> > > > > > > > > > > > > ret =3D
> > > > > > > > > > > > > probe_kernel_address(regs->nip, inst);
> > > > > > > > > > > > >=20
> > > > > > > > > > > > > However, the kernel still locked up after fixing =
that.
> > > > > > > > > > > > > Now I wonder why this fixup is there in the first=
place?
> > > > > > > > > > > > > The routine will not really fixup the insn, just
> > > > > > > > > > > > > return 0xffffffff for the failing read and then a=
dvance the
> >=20
> > process NIP.
> > > > > > > > > > >=20
> > > > > > > > > > > You are right. The code here only gives 0xffffffff t=
o
> > > > > > > > > > > the load instructions and
> > > > > > > > > >=20
> > > > > > > > > > continue with the next instruction when the load
> > > > > > > > > > instruction is causing the machine check. This will
> > > > > > > > > > prevent a system lockup when reading from PCI/RapidIO d=
evice
> >=20
> > which is link down.
> > > > > > > > > > >=20
> > > > > > > > > > > I don't know what is actual problem in your case.
> > > > > > > > > > > Maybe it is a write
> > > > > > > > > >=20
> > > > > > > > > > instruction instead of read? Or the code is in a infi=
nite loop
> >=20
> > waiting for
> > > > >=20
> > > > > a
> > > > > > > >=20
> > > > > > > > valid
> > > > > > > > > > read result? Are you able to do some further debugging
> > > > > > > > > > with the NIP correctly printed?
> > > > > > > > > > >=20
> > > > > > > > > >=20
> > > > > > > > > > According to the MC it is a Read and the NIP also leads
> > > > > > > > > > to a read in the
> > > > > > > >=20
> > > > > > > > program.
> > > > > > > > > > ATM, I have disabled the fixup but I will enable that a=
gain.
> > > > > > > > > > Question, is it safe add a small printk when this MC
> > > > > > > > > > happens(after fixing up)? I need to see that it has
> > > > > > > > > > happened as the error is somewhat
> > > > > > > >=20
> > > > > > > > random.
> > > > > > > > >=20
> > > > > > > > > I think it is safe to add printk as the current machine
> > > > > > > > > check handlers are also
> > > > > > > >=20
> > > > > > > > using printk.
> > > > > > > >=20
> > > > > > > > I hope so, but if the fixup fires there is no printk at all=
so I was a bit
> >=20
> > unsure.
> > > > > > > > Don't like this fixup though, is there not a better way tha=
n
> > > > > > > > faking a read to user space(or kernel for that matter) ?
> > > > > > >=20
> > > > > > > I don't have a better idea. Without the fixup, the offending
> > > > > > > load instruction
> > > > >=20
> > > > > will never finish if there is anything wrong with the backing
> > > > > device and freeze the whole system. Do you have any suggestion i=
n mind?
> > > > > > >=20
> > > > > >=20
> > > > > > But it never finishes the load, it just fakes a load of
> > > > > > 0xfffffffff, for user space I rather have it signal a SIGBUS bu=
t
> > > > > > that does not seem to work either, at least not for us but that
> > > > > > could be a bug in general MC code
> > > > >=20
> > > > > maybe.
> > > > > > This fixup might be valid for kernel only as it has never worke=
d
> > > > > > for user space
> > > > >=20
> > > > > due to the bug I found.
> > > > > >=20
> > > > > > Where can I read about this errata ?
> > > > >=20
> > > > > I have look high and low an cannot find an errata which maps to t=
his fixup.
> > > > > The closest I get is A-005125 which seems to have another
> > > > > workaround, I cannot find any evidence that this workaround has b=
een
> >=20
> > applied in Linux, can you?
> > > >=20
> > > > This is not A-005125. There was an erratum for this issue with old=
er silicons
> >=20
> > (e.g. erratum PCI-ex 3 for MPC8572).
> > > > " When its link goes down, the PCI Express controller clears all
> > > > outstanding transactions with an error indicator and sends a link
> > > > down exception to the interrupt controller if PEX_PME_MES_DISR[LDDD=
]
> > > > =3D 0. If, however, any transactions are sent to the controller aft=
er
> > > > the link down event, they are accepted by the controller and wait
> > > > for the link to come back up before starting any timeout counters (=
for
> >=20
> > example, completion timeout). There is no mechanism to cancel the new
> > transactions short of a device HRESET. "
> > > >=20
> > > > But it was removed in newer silicon like P2020/P2010 probably becau=
se a
> >=20
> > Machine Check will be triggered in this situation to deal with the stal=
led
> > instruction and no longer considered it as a hardware issue.
> > > >=20
> > >=20
> > > Maybe this fixup should be configurable then?
>=20
> No. My point is that the problem was no longer considered a hardware iss=
ue because of the machine check mechanism is in place to handle it. If the=
re is no handling of this special case, we would still experience a system =
hang if this situation really occurs.
>=20
> > >=20
> > > > The A-005125 is dealt with in u-boot.
> >=20
> > https://emea01.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Fli=
sts.de
> > nx.de%2Fpipermail%2Fu-boot%2F2013-
> > August%2F161185.html&data=3D01%7C01%7Cleoyang.li%40nxp.com%7Ccb8a93e
> > 0090e48eb53a008d4f6b84235%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0&
> > sdata=3D8sR4yoXA4adqMHz6TY%2BvmYpfCBTcYEZHjPuANjz%2F1EQ%3D&reserve
> > d=3D0
> > >=20
> > > Yes, I found it eventually :)
> > >=20
> > > However, I cannot return to normal execution. I can follow the code t=
o
> > > returning from
> > > machine_check_exception() and moving into ASM handler for returning
> > > from a ME but then I am a bit lost. It does not seem to be any proble=
m
> > > executing, it feels more like a SW bug dealing with machine checks. D=
on't
> >=20
> > known how to diagnose this further and could use some pointers.
>=20
> Is the execution returned to the user application? I doubt the system ha=
ng is caused by the machine check handling.
> You can try to comment out the machine check handling code and check if t=
here is any improvement and see if
> this is related to the machine check handling.
It tries to return to user app but I cannot see what happens as the system =
lock up when the
MC returns.
How do you mean comment out MC handling? The simplest path is the PCI fixup=
which will
just do regs->nip +=3D 4; and then return to user space. That still does no=
t work as
as soon MC handling returns, the system is locked up.
>=20
> Machine check is a serious situation and not always possible to be recove=
red from.=20
This one should at least not kill the whole system. It is a simple bus erro=
r in user space and
the app should get SIGBUS and the the system should carry on.=20
> I would focus more on debugging why the machine check is triggered by the=
user space application.
> Can you locate what code is causing this machine check from user space? =
=20
> Is it accessing some hardware related space which is not ready?=20
> Or is it accessing address that it shouldn't have accessed?
of course, this is ongoing and getting closer a solution. The MC looking th=
e machine completely
does not make this any easier though.
These are 2 separate things, fixing the cause and not having a simple bus e=
rror lock up the machine.
I am focusing on fixing the lockup.
I have been following the execution in the kernel and I always end up in th=
e ASM returning
from the MC.
The other day we got a similar PCI MC(bus error) on T1042 CPU(e5500/e500mc)=
and there
the system survived. The one thing I see different there is that MSR RI is =
set
when entering MC, why is that?
Jocke=
next prev parent reply other threads:[~2017-09-09 12:45 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-01 11:32 Machine Check in P2010(e500v2) Joakim Tjernlund
2017-09-05 8:40 ` Joakim Tjernlund
2017-09-06 15:38 ` York Sun
2017-09-06 19:31 ` Leo Li
2017-09-06 20:17 ` Joakim Tjernlund
2017-09-06 20:28 ` Leo Li
2017-09-06 20:53 ` Joakim Tjernlund
2017-09-06 21:13 ` Leo Li
2017-09-06 22:50 ` Joakim Tjernlund
2017-09-07 8:41 ` Joakim Tjernlund
2017-09-07 18:54 ` Leo Li
2017-09-08 9:54 ` Joakim Tjernlund
2017-09-08 12:50 ` Joakim Tjernlund
2017-09-08 22:27 ` Leo Li
2017-09-09 12:45 ` Joakim Tjernlund [this message]
[not found] ` <1504961965.31322.72.camel@infinera.com>
2017-09-14 16:55 ` Joakim Tjernlund
2017-09-20 16:45 ` Joakim Tjernlund
2017-09-21 18:53 ` Leo Li
2017-09-06 10:05 ` Laurentiu Tudor
2017-09-06 10:16 ` Joakim Tjernlund
2017-09-08 1:56 ` Scott Wood
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