linux-kernel - Re: The current SME implementation fails kexec/kdump kernel booting.

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Date:   Tue, 11 Jun 2019 17:52:55 +0800
From:   lijiang <lijiang@...hat.com>
To:     "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        Baoquan He <bhe@...hat.com>
Cc:     "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: The current SME implementation fails kexec/kdump kernel booting.

在 2019年06月09日 11:45, lijiang 写道:
> 在 2019年06月06日 00:04, Lendacky, Thomas 写道:
>> On 6/4/19 7:56 PM, Baoquan He wrote:
>>> On 06/04/19 at 03:56pm, Lendacky, Thomas wrote:
>>>> On 6/4/19 8:49 AM, Baoquan He wrote:
>>>>> Hi Tom,
>>>>>
>>>>> Lianbo reported kdump kernel can't boot well with 'nokaslr' added, and
>>>>> have to enable KASLR in kdump kernel to make it boot successfully. This
>>>>> blocked his work on enabling sme for kexec/kdump. And on some machines
>>>>> SME kernel can't boot in 1st kernel.
>>>>>
>>>>> I checked code of SME implementation, and found out the root cause. The
>>>>> above failures are caused by SME code, sme_encrypt_kernel(). In
>>>>> sme_encrypt_kernel(), you get a 2M of encryption work area as intermediate
>>>>> buffer to encrypt kernel in-place. And the work area is just after _end of
>>>>> kernel.
>>>>
>>>> I remember worrying about something like this back when I was testing the
>>>> kexec support. I had come up with a patch to address it, but never got the
>>>> time to test and submit it.  I've included it here if you'd like to test
>>>> it (I haven't done run this patch in quite some time). If it works, we can
>>>> think about submitting it.
>>>
>>> Thanks for your quick response and making this patch, Tom.
>>>
>>> Tested on a speedway machine, it entered into kernel, but failed in
>>> below stage. Tested two times, always happened.
>>
>> Is this the initial kernel boot or the kexec kernel boot?
>>
>> It looks like this is related to the initrd/initramfs decryption. Not
>> sure what could be happening there. I just tried the patch on my Naples
>> system and a 5.2.0-rc3 kernel and have been able to repeatedly kexec boot
>> a number of times so far.
>>
> 
> I used the hacked kexec-tools(by Baoquan) to test it, the kexec-d kernel and
> kdump kernel worked well. But Tom's patch only worked for the kexec-d kernel,
> and the kdump kernel did not work(kdump kernel could not successfully boot).
> What's the difference between them?
> 

After applied Tom's patch, i changed the reserved memory(for crash kernel) to the
above 256M(>256M), such as crashkernel=320M or 384M,512M..., the kdump kernel can
work and successfully dump the vmcore.

But the kdump kernel always happened the panic or could not boot successfully in
the 256M(<= 256M) case, and on HP machine, i noticed that it printed OOM, the kdump
kernel was too smaller memory. But i never see the OOM on speedway machine(probably
related to the earlyprintk, it doesn't work and it loses many logs).

After removing the option 'CONFIG_DEBUG_INFO' from .config, i tested again, the kdump
kernel did not happen the panic in the 256M(crashkernel=256M), the kdump kernel can
work and succeed to dump the vmcore on HP machine or speedway machine.

It seems that the small memory caused the previous failure in kdump kernel. I would
suggest to post this patch to upstream. What's your opinion? Tom, Baoquan and other
people. Or do you have any comment?

Thanks.
Lianbo

> Thanks
> Lianbo
> 
>> Thanks,
>> Tom
>>
>>>
>>>
>>> [    4.978521] Freeing unused decrypted memory: 2040K
>>> [    4.983800] Freeing unused kernel image memory: 2344K
>>> [    4.988943] Write protecting the kernel read-only data: 18432k
>>> [    4.995306] Freeing unused kernel image memory: 2012K
>>> [    5.000488] Freeing unused kernel image memory: 256K
>>> [    5.005540] Run /init as init process
>>> [    5.009443] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00
>>> [    5.017230] CPU: 0 PID: 1 Comm: init Not tainted 5.2.0-rc2+ #38
>>> [    5.023251] Hardware name: AMD Corporation Speedway/Speedway, BIOS RSW1004B 10/18/2017
>>> [    5.031299] Call Trace:
>>> [    5.033793]  dump_stack+0x46/0x60
>>> [    5.037169]  panic+0xfb/0x2cb
>>> [    5.040191]  do_exit.cold.21+0x59/0x81
>>> [    5.044004]  do_group_exit+0x3a/0xa0
>>> [    5.047640]  __x64_sys_exit_group+0x14/0x20
>>> [    5.051899]  do_syscall_64+0x55/0x1c0
>>> [    5.055627]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>> [    5.060764] RIP: 0033:0x7fa1b1fc9e2e
>>> [    5.064404] Code: Bad RIP value.
>>> [    5.067687] RSP: 002b:00007fffc5abb778 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
>>> [    5.075296] RAX: ffffffffffffffda RBX: 00007fa1b1fd2528 RCX: 00007fa1b1fc9e2e
>>> [    5.082625] RDX: 000000000000007f RSI: 000000000000003c RDI: 000000000000007f
>>> [    5.089879] RBP: 00007fa1b21d8d00 R08: 00000000000000e7 R09: 00007fffc5abb688
>>> [    5.097134] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002
>>> [    5.104386] R13: 0000000000000001 R14: 00007fa1b21d8d40 R15: 00007fa1b21d8d30
>>> [    5.111645] Kernel Offset: disabled
>>> [    5.423002] Rebooting in 10 seconds..
>>> [   15.429641] ACPI MEMORY or I/O RESET_REG.
>>>