Re: [RFC Patch 25/25] sync mmu before resuming secondary vm

[Wen Congyang <wency@cn.fujitsu.com>]

At 07/24/2014 06:59 PM, Tim Deegan Write:
> At 19:39 +0800 on 18 Jul (1405708750), Wen Congyang wrote:
>> In out test, we find secondary vm will be bluescreen due to memory
>> related problem. If we sync mmu, the problem will disappear.
> 
> Erk.  Do you understand _why_ this happens?  Do you need both the TLB
> flush and the EPT flush to fix it?  

I cannot reproduce this problem now. But Some user processes will exited
due to memory problem.

Secondary vm is running like this:
1. running
2. stop
3. update the the state(both memory and device)
4. continue running

Before step4, I think the tlb for the guest is out-of-data.
I don't have any knowledge about EPT. So I don't know if the
ept is out-of-data too.

Anyway, I will remove this patch in next version.

Thanks
Wen Congyang

> 
> The TLB flush sounds plausible because the migration may have changed
> some pagetables and you've elided any TLB flushes that happened on the
> source.  For that case I think I'd prefer to make the TLB flush
> implicit in the HVM load operation, e.g., by putting a call to
> hvm_asid_flush_vcpu(v) into hvm_load_cpu_ctxt() (on the grounds that the
> TLB is part of the vcpu state).
> 
> Cheers,
> 
> Tim.
>