Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:
> On 09/03/20 07:57, Thomas Gleixner wrote:
>> Thomas Gleixner <tglx@xxxxxxxxxxxxx> writes:
>>
>> guest side:
>>
>> nmi()/mce() ...
>>
>> stash_crs();
>>
>> + stash_and_clear_apf_reason();
>>
>> ....
>>
>> + restore_apf_reason();
>>
>> restore_cr2();
>>
>> Too obvious, isn't it?
>
> Yes, this works but Andy was not happy about adding more
> save-and-restore to NMIs. If you do not want to do that, I'm okay with
> disabling async page fault support for now.
I'm fine with doing that save/restore dance, but I have no strong
opinion either.
> Storing the page fault reason in memory was not a good idea. Better
> options would be to co-opt the page fault error code (e.g. store the
> reason in bits 31:16, mark bits 15:0 with the invalid error code
> RSVD=1/P=0), or to use the virtualization exception area.
Memory store is not the problem. The real problem is hijacking #PF.
If you'd have just used a separate VECTOR_ASYNC_PF then none of these
problems would exist at all.
Thanks,
tglx
