On Thu, 2017-09-07 at 18:54 +0000, Leo Li wrote: > > -----Original Message----- > > From: Joakim Tjernlund [mailto:joakim.tjernl...@infinera.com] > > Sent: Thursday, September 07, 2017 3:41 AM > > To: linuxppc-dev@lists.ozlabs.org; Leo Li <leoyang...@nxp.com>; York Sun > > <york....@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.tjernl...@infinera.com] > > > > > Sent: Wednesday, September 06, 2017 3:54 PM > > > > > To: linuxppc-dev@lists.ozlabs.org; Leo Li <leoyang...@nxp.com>; > > > > > York Sun <york....@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.tjernl...@infinera.com] > > > > > > > Sent: Wednesday, September 06, 2017 3:17 PM > > > > > > > To: linuxppc-dev@lists.ozlabs.org; Leo Li > > > > > > > <leoyang...@nxp.com>; York Sun <york....@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.tjernl...@infinera.com>; > > > > > > > > > linuxppc- d...@lists.ozlabs.org; Leo Li > > > > > > > > > <leoyang...@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. >
Maybe this fixup should be configurable then? > The A-005125 is dealt with in u-boot. > https://lists.denx.de/pipermail/u-boot/2013-August/161185.html Yes, I found it eventually :) However, I cannot return to normal execution. I can follow the code to 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 problem executing, it feels more like a SW bug dealing with machine checks. Don't known how to diagnose this further and could use some pointers. Jocke
