Re: [PATCH v3 01/11] xen/manage: keep track of the on-going suspend mode

[boris.ostrovsky@xxxxxxxxxx]

On 9/25/20 6:28 PM, Anchal Agarwal wrote:
> On Fri, Sep 25, 2020 at 04:02:58PM -0400, boris.ostrovsky@xxxxxxxxxx wrote:
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>> On 9/25/20 3:04 PM, Anchal Agarwal wrote:
>>> On Tue, Sep 22, 2020 at 11:17:36PM +0000, Anchal Agarwal wrote:
>>>> On Tue, Sep 22, 2020 at 12:18:05PM -0400, boris.ostrovsky@xxxxxxxxxx wrote:
>>>>> CAUTION: This email originated from outside of the organization. Do not 
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>>>>> know the content is safe.
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>>>>>
>>>>> On 9/21/20 5:54 PM, Anchal Agarwal wrote:

>>>>> Also, wrt KASLR stuff, that issue is still seen sometimes but I haven't 
>>>>> had
>>>>> bandwidth to dive deep into the issue and fix it.
>>
>> So what's the plan there? You first mentioned this issue early this year and 
>> judged by your response it is not clear whether you will ever spend time 
>> looking at it.
>>
> I do want to fix it and did do some debugging earlier this year just haven't
> gotten back to it. Also, wanted to understand if the issue is a blocker to 
> this
> series?


Integrating code with known bugs is less than ideal.


3% failure for this feature seems to be a manageable number from the 
reproducability perspective --- you should be able to script this and each 
iteration should take way under a minute, no?


> I had some theories when debugging around this like if the random base 
> address picked by kaslr for the
> resuming kernel mismatches the suspended kernel and just jogging my memory, I 
> didn't find that as the case.
> Another hunch was if physical address of registered vcpu info at boot is 
> different from what suspended kernel
> has and that can cause CPU's to get stuck when coming online. 


I'd think if this were the case you'd have 100% failure rate. And we are also 
re-registering vcpu info on xen restore and I am not aware of any failures due 
to KASLR.


> The issue was only
> reproducible 3% of the time out of 3000 runs hence its hard to just reproduce 
> this.
>
> Moreover, I also wanted to get an insight on if hibernation works correctly 
> with KASLR
> generally and its only Xen causing the issue?


With KASLR being on by default I'd be surprised if it didn't.


-boris