Re: [Qemu-devel] [PATCH v1 00/17] Background snapshots

[Denis Plotnikov <dplotnikov@virtuozzo.com>]

Hi Peter,

Thanks for the reply.

Ok, I understand about tcg.
So my only option is to wait for userfaultfd-wp.
Do you know if anyone is  currently working on this? And if so, then is 
there any estimations when the userfaultfd is ready?

Denis


On 05.09.2018 06:32, Peter Xu wrote:
> On Tue, Sep 04, 2018 at 04:00:31PM +0300, Denis Plotnikov wrote:
>> Hi Peter
> 
> Hi, Denis,
> 
>>
>> I moved the code to the repository
>> https://github.com/denis-plotnikov/qemu/tree/background-snapshot-kvm.
>> the current version includes fixes with respect to your comments for version
>> 1.
>> I moved KVM related patches to the end of the branch (formerly patch
>> series).
>> Since, the KVM patches and the other parts to modify (vhost an others) are
>> needless in favor of upcoming userfaltfd,
>> I would ask you to review the general framework which is able to work with
>> tcg.
>>
>> Thanks in advance!
> 
> Thank you for pushing the tree.
> 
> I might have made a mistake before that I thought this work is at
> least working for TCG, but I think I was wrong.  The problem is (I'm
> trying to repeat Dave's question that you seems haven't yet answered):
> even for TCG there could be use cases where the process might access
> guest memory from the kernel space (e.g., vhost, or any system calls
> that with a guest memory buffer passed in).  I'm afraid mprotect() and
> the whole signal-based mechanism cannot be able to address these page
> faults, then we'll encounter adhoc errors and we'll need to fix all
> these places up.  Userfaultfd-wp should not have this problem.
> 
> I think the general idea of the work is good, but I'm not sure whether
> we can merge the work if we don't settle these issues.
> 
> Regards,
> 

-- 
Best,
Denis