Machine Check in P2010(e500v2)
Leo Li
leoyang.li at nxp.com
Fri Sep 8 04:54:31 AEST 2017
> -----Original Message-----
> From: Joakim Tjernlund [mailto:Joakim.Tjernlund at infinera.com]
> Sent: Thursday, September 07, 2017 3:41 AM
> To: linuxppc-dev at lists.ozlabs.org; Leo Li <leoyang.li at nxp.com>; York Sun
> <york.sun at nxp.com>
> Subject: Re: Machine Check in P2010(e500v2)
>
> 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 at infinera.com]
> > > > Sent: Wednesday, September 06, 2017 3:54 PM
> > > > To: linuxppc-dev at lists.ozlabs.org; Leo Li <leoyang.li at nxp.com>;
> > > > York Sun <york.sun at nxp.com>
> > > > Subject: Re: Machine Check in P2010(e500v2)
> > > >
> > > > On Wed, 2017-09-06 at 20:28 +0000, Leo Li wrote:
> > > > > > -----Original Message-----
> > > > > > From: Joakim Tjernlund [mailto:Joakim.Tjernlund at infinera.com]
> > > > > > Sent: Wednesday, September 06, 2017 3:17 PM
> > > > > > To: linuxppc-dev at lists.ozlabs.org; Leo Li
> > > > > > <leoyang.li at nxp.com>; York Sun <york.sun at nxp.com>
> > > > > > Subject: Re: Machine Check in P2010(e500v2)
> > > > > >
> > > > > > 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 at infinera.com>;
> > > > > > > > linuxppc- dev at lists.ozlabs.org; Leo Li
> > > > > > > > <leoyang.li at nxp.com>
> > > > > > > > Subject: Re: Machine Check in P2010(e500v2)
> > > > > > > >
> > > > > > > > Scott is no longer with Freescale/NXP. Adding Leo.
> > > > > > > >
> > > > > > > > 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
> > > >
> > > > *regs)
> > > > > > > > > if (is_in_pci_mem_space(addr)) {
> > > > > > > > > if (user_mode(regs)) {
> > > > > > > > > pagefault_disable();
> > > > > > > > > - ret = get_user(regs->nip, &inst);
> > > > > > > > > + ret = get_user(inst, (__u32
> > > > > > > > > + __user *)regs->nip);
> > > > > > > > > pagefault_enable();
> > > > > > > > > } else {
> > > > > > > > > ret =
> > > > > > > > > probe_kernel_address(regs->nip, inst);
> > > > > > > > >
> > > > > > > > > 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 advance the process NIP.
> > > > > > >
> > > > > > > You are right. The code here only gives 0xffffffff to the
> > > > > > > load instructions and
> > > > > >
> > > > > > 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 device which is link down.
> > > > > > >
> > > > > > > I don't know what is actual problem in your case. Maybe it
> > > > > > > is a write
> > > > > >
> > > > > > instruction instead of read? Or the code is in a infinite loop waiting for
> a
> > > >
> > > > valid
> > > > > > read result? Are you able to do some further debugging with
> > > > > > the NIP correctly printed?
> > > > > > >
> > > > > >
> > > > > > According to the MC it is a Read and the NIP also leads to a
> > > > > > read in the
> > > >
> > > > program.
> > > > > > ATM, I have disabled the fixup but I will enable that again.
> > > > > > 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
> > > >
> > > > random.
> > > > >
> > > > > I think it is safe to add printk as the current machine check
> > > > > handlers are also
> > > >
> > > > using printk.
> > > >
> > > > I hope so, but if the fixup fires there is no printk at all so I was a bit unsure.
> > > > Don't like this fixup though, is there not a better way than
> > > > faking a read to user space(or kernel for that matter) ?
> > >
> > > I don't have a better idea. Without the fixup, the offending load instruction
> will never finish if there is anything wrong with the backing device and freeze the
> whole system. Do you have any suggestion in mind?
> > >
> >
> > But it never finishes the load, it just fakes a load of 0xfffffffff,
> > for user space I rather have it signal a SIGBUS but that does not seem
> > to work either, at least not for us but that could be a bug in general MC code
> maybe.
> > This fixup might be valid for kernel only as it has never worked for user space
> due to the bug I found.
> >
> > Where can I read about this errata ?
>
> I have look high and low an cannot find an errata which maps to this fixup.
> The closest I get is A-005125 which seems to have another workaround, I cannot
> find any evidence that this workaround has been applied in Linux, can you?
This is not A-005125. There was an erratum for this issue with older silicons (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] = 0. If, however, any transactions are sent to the controller after
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 example, completion timeout). There is no mechanism to
cancel the new transactions short of a device HRESET. "
But it was removed in newer silicon like P2020/P2010 probably because a Machine Check will be triggered in this situation to deal with the stalled instruction and no longer considered it as a hardware issue.
The A-005125 is dealt with in u-boot. https://lists.denx.de/pipermail/u-boot/2013-August/161185.html
Regards,
Leo
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