Re: çå: çå: loop nesting in alignment exception and machine check

[Christophe Leroy]

Hi,

Le 01/11/2019 Ã 02:57, Wangshaobo (bobo) a ÃcritÂ:
> Hi, Christophe
>
> 	I am sorry that we are in some troubles for some unpredictable problems when we replay and haven't given you a quick reply.
> 	
> 	I also want to ask does the phenomeon(use memcpy_toio when copy ioremap_address) only occurs in powerpc ? does any other
> arch also has the same problem ? we are in persuit of asking why this phenomenon happened. Our linux kernel version is 4.4.

It's not a problem ... it's a feature.

I have no idea whether the same kind of issue can happen on other 
arches, sorry.

Christophe

> 	
> 	thanks very much.
>
> -----éäåä-----
> åää: Christophe Leroy [mailto:christophe.leroy@xxxxxx]
> åéæé: 2019å10æ31æ 19:13
> æää: Wangshaobo (bobo) <bobo.shaobowang@xxxxxxxxxx>
> æé: chengjian (D) <cj.chengjian@xxxxxxxxxx>; Libin (Huawei) <huawei.libin@xxxxxxxxxx>; Xiexiuqi <xiexiuqi@xxxxxxxxxx>; zhangyi (F) <yi.zhang@xxxxxxxxxx>
> äé: Re: çå: loop nesting in alignment exception and machine check
>
> Hi,
>
> Did you try ? Does it work ?
>
> Christophe
>
> Le 28/10/2019 Ã 06:57, Wangshaobo (bobo) a ÃcritÂ:
> > Hi,Christophe
> >
> > Thank you for your quick reply. I will try to use memcpy_toio() instead of memcpy().
> >
> > -----éäåä-----
> > åää: Christophe Leroy [mailto:christophe.leroy@xxxxxx]
> > åéæé: 2019å10æ26æ 19:20
> > æää: Wangshaobo (bobo) <bobo.shaobowang@xxxxxxxxxx>
> > æé: linux-arch@xxxxxxxxxxxxxxx; alistair@xxxxxxxxxxxx; chengjian (D)
> > <cj.chengjian@xxxxxxxxxx>; Xiexiuqi <xiexiuqi@xxxxxxxxxx>;
> > linux-kernel@xxxxxxxxxxxxxxx; oss@xxxxxxxxxxxx; paulus@xxxxxxxxx;
> > Libin (Huawei) <huawei.libin@xxxxxxxxxx>; agust@xxxxxxx;
> > linuxppc-dev@xxxxxxxxxxxxxxxx
> > äé: Re: loop nesting in alignment exception and machine check
> >
> > Hi,
> >
> > Le 26/10/2019 Ã 09:23, Wangshaobo (bobo) a ÃcritÂ:
> > > Hi,
> > >
> > > I encountered a problem about a loop nesting occurred in
> > > manufacturing the alignment exception in machine check, trigger background is :
> > >
> > > problem:
> > >
> > > machine checkout or critical interrupt ->â->kbox_write[for recording
> > > last words] -> memcpy(irremap_addr, src,size):_GLOBAL(memcpy)â
> > >
> > > when we enter memcpy,a command âdcbz r11,r6â will cause a alignment
> > > exception, in this situation,r11 loads the ioremap address,which
> > > leads to the alignment exception,
> >
> > You can't use memcpy() on something else than memory.
> >
> > For an ioremapped area, you have to use memcpy_toio()
> >
> > Christophe
> >
> > > then the command can not be process successfully,as we still in
> > > machine check.at the end ,it triggers a new irq machine check in irq
> > > handler function,a loop nesting begins.
> > >
> > > analysis:
> > >
> > > We have analysed a lot,but it still can not come to a reasonable
> > > description,in common,the alignment triggered in machine check
> > > context can still be collected into the Kbox
> > >
> > > after alignment exception be handled by handler function, but how
> > > does the machine checkout can be triggered in the handler fucntion
> > > for any causes? We print relevant registers
> > >
> > > as follow when first enter machine check and alignment exception
> > > handler
> > > function:
> > >
> > >    ÂÂÂÂÂÂÂÂ MSR:0x2ÂÂÂÂÂ MSR:0x0
> > >
> > >    ÂÂÂÂÂÂÂÂ SRR1:0x2ÂÂÂÂÂ SRR1:0x21002
> > >
> > >    ÂÂÂÂÂÂÂÂ But the manual says SRR1 should be set to MSR(0x2),why
> > > that happened ?
> > >
> > >    ÂÂÂÂÂÂÂÂ Then a branch in handler function copy the SRR1 to
> > > MSR,this enble MSR[ME] and MSR[CE],system collapses.
> > >
> > > Conclusion:
> > >
> > >    ÂÂÂÂÂÂÂÂ 1)Â why the alignment exception can not be handled in
> > > machine check ?
> > >
> > >    ÂÂÂÂÂÂÂÂ 2)Â besides memcpy,any other function can cause the
> > > alignment exception ?
> > >
> > > We still recurrent it, the line as follows:
> > >
> > >    ÂÂÂÂÂÂÂÂ Cpu dead lock->watch log->trigger
> > > fiq->kbox_write->memcpy->alignment exception->print last words.
> > >
> > >    ÂÂÂÂÂÂÂÂ but for those problems as below,what the kbox printed is empty.
> > >
> > > ------------------kbox restart:[ÂÂ 10.147594]----------------
> > >
> > > kbox verify fs magic fail
> > >
> > > kbox mem mabye destroyed, format it
> > >
> > > kbox: load OK
> > >
> > > lock-task: major[249] minor[0]
> > >
> > > -----start show_destroyed_kbox_mem_head----
> > >
> > > 00000000: 00000000 00000000 00000000 00000000Â ................
> > >
> > > 00000010: 00000000 00000000 00000000 00000000Â ................
> > >
> > > 00000020: 00000000 00000000 00000000 00000000Â ................
> > >
> > > 00000030: 00000000 00000000 00000000 00000000Â ................
> > >
> > > 00000040: 00000000 00000000 00000000 00000000Â ................
> > >
> > > 00000050: 00000000 00000000 00000000 00000000Â ................
> > >
> > > 00000060: 00000000 00000000 00000000 00000000Â ................
> > >
> > > 00000070: 00000000 00000000 00000000 00000000Â ................
> > >
> > > 00000080: 00000000 00000000 00000000 00000000Â ................
> > >
> > > 00000090: 00000000 00000000 00000000 00000000Â ................