linux-kernel - Re: [PATCH v2] x86/mce: Fix endless loop when run task works after #MC

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Wed, 7 Jul 2021 17:51:20 +0800
From:   Ding Hui <dinghui@...gfor.com.cn>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     bp@...en8.de, bp@...e.de, naoya.horiguchi@....com,
        osalvador@...e.de, peterz@...radead.org,
        linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
        hpa@...or.com, youquan.song@...el.com, huangcun@...gfor.com.cn,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] x86/mce: Fix endless loop when run task works after
 #MC

On 2021/7/7 11:39, Ding Hui wrote:
> On 2021/7/7 0:44, Luck, Tony wrote:
>> On Tue, Jul 06, 2021 at 08:16:06PM +0800, Ding Hui wrote:
>>> Recently we encounter multi #MC on the same task when it's
>>> task_work_run() has not been called, current->mce_kill_me was
>>> added to task_works list more than once, that make a circular
>>> linked task_works, so task_work_run() will do a endless loop.
>>
>> I saw the same and posted a similar fix a while back:
>>
>> https://www.spinics.net/lists/linux-mm/msg251006.html
>>
>> It didn't get merged because some validation tests began failing
>> around the same time.  I'm now pretty sure I understand what happened
>> with those other tests.
>>
>> I'll post my updated version (second patch in a three part series)
>> later today.
>>
> 
> Thanks for your fixes.
> 
> After digging my original problem, maybe I find out why I met #MC flood.
> 
> My test case:
> 1. run qemu-kvm guest VM, OS is memtest86+.iso
> 2. inject SRAR UE to VM memory and wait #MC
> When VM trigger #MC, I expect that qemu will receive SIGBUS signal ASAP, 
> and with the modifed qemu, I will kill VM.
> 
> In this case, do_machine_check() maybe called by kvm_machine_check() in 
> vmx.c.
> 
> Before [1], memory_failure() is called in do_machine_check(), so 
> TIF_SIGPENDING is set on due to SIGBUS signal, vcpu_run() checked the 
> pending singal, so return to qemu to handle SIGBUS.
> 
> After [1], do_machine_check() only add task work but not send SIGBUS 
> directly, vcpu_run() will not break the for-loop because 
> vcpu_enter_guest() return 1 and not set TIF_SIGPENDING on, task works 
> never executed until sth else happen. So the kvm enter guest repeatedly 
> and the #MC is triggered repeatedly.
> 

Sorry for my incorrect description.

I figure out that my test kernel is not the lastest, it's without [2] 
commit 72c3c0fe54a3 （"x86/kvm: Use generic xfer to guest work 
function"), so vcpu_run() only care about signal_pending but not 
TIF_NOTIFY_RESUME which set on in task_work_add().

After [2], #MC flood should not exist.

Also thank Thomas Gleixner.

> Can you consider to fix cases like this?
> 
> And do you mind to give me some advice for my temporary workaround about 
> this #MC flood:
> I want to check the context of do_machine_check() is exception or kvm, 
> and fallback to call kill_me_xxx directly when in kvm context. (I 
> already tested simply and met my expection)
> 

So ignore my ask, please.

> [1]: commit 5567d11c21a1 ("x86/mce: Send #MC singal from task work")


-- 
Thanks,
- Ding Hui