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Subject: Re: loop nesting in alignment exception and machine check
To:     "Wangshaobo (bobo)" <bobo.shaobowang@huawei.com>
Cc:     "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "alistair@popple.id.au" <alistair@popple.id.au>,
        "chengjian (D)" <cj.chengjian@huawei.com>,
        Xiexiuqi <xiexiuqi@huawei.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "oss@buserror.net" <oss@buserror.net>,
        "paulus@samba.org" <paulus@samba.org>,
        "Libin (Huawei)" <huawei.libin@huawei.com>,
        "agust@denx.de" <agust@denx.de>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
References: <D44062DC474617438D5181ADFE2B2C21016DE42A@dggemi529-mbs.china.huawei.com>
From:   Christophe Leroy <christophe.leroy@c-s.fr>
Message-ID: <8215aeb3-57dd-223a-29d3-45ca22b0543c@c-s.fr>
Date:   Sat, 26 Oct 2019 13:20:06 +0200
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Hi,

Le 26/10/2019 ? 09:23, Wangshaobo (bobo) a ?crit?:
> 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 ->?->kbox_write[for recording 
> last words] -> memcpy(irremap_addr, src,size):_GLOBAL(memcpy)?
> 
> when we enter memcpy,a command ?dcbz r11,r6? 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:
> 
>  ???????? MSR:0x2????? MSR:0x0
> 
>  ???????? SRR1:0x2????? SRR1:0x21002
> 
>  ???????? But the manual says SRR1 should be set to MSR(0x2),why that 
> happened ?
> 
>  ???????? Then a branch in handler function copy the SRR1 to MSR,this 
> enble MSR[ME] and MSR[CE],system collapses.
> 
> Conclusion:
> 
>  ???????? 1)? why the alignment exception can not be handled in machine 
> check ?
> 
>  ???????? 2)? besides memcpy,any other function can cause the alignment 
> exception ?
> 
> We still recurrent it, the line as follows:
> 
>  ???????? Cpu dead lock->watch log->trigger 
> fiq->kbox_write->memcpy->alignment exception->print last words.
> 
>  ???????? but for those problems as below,what the kbox printed is empty.
> 
> ------------------kbox restart:[?? 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 00000000? ................
> 
> 00000010: 00000000 00000000 00000000 00000000? ................
> 
> 00000020: 00000000 00000000 00000000 00000000? ................
> 
> 00000030: 00000000 00000000 00000000 00000000? ................
> 
> 00000040: 00000000 00000000 00000000 00000000? ................
> 
> 00000050: 00000000 00000000 00000000 00000000? ................
> 
> 00000060: 00000000 00000000 00000000 00000000? ................
> 
> 00000070: 00000000 00000000 00000000 00000000? ................
> 
> 00000080: 00000000 00000000 00000000 00000000? ................
> 
> 00000090: 00000000 00000000 00000000 00000000? ................
>