Re: [PATCH v2] x86/kvm: Disable KVM_ASYNC_PF_SEND_ALWAYS

[Andy Lutomirski]

> On Apr 6, 2020, at 1:25 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> ïOn Mon, Apr 06, 2020 at 03:09:51PM -0400, Vivek Goyal wrote:
>>> On Mon, Mar 09, 2020 at 09:22:15PM +0100, Peter Zijlstra wrote:
>>> On Mon, Mar 09, 2020 at 08:05:18PM +0100, Thomas Gleixner wrote:
>>>> Andy Lutomirski <luto@xxxxxxxxxx> writes:
>>> 
>>>>> I'm okay with the save/restore dance, I guess.  It's just yet more
>>>>> entry crud to deal with architecture nastiness, except that this
>>>>> nastiness is 100% software and isn't Intel/AMD's fault.
>>>> 
>>>> And we can do it in C and don't have to fiddle with it in the ASM
>>>> maze.
>>> 
>>> Right; I'd still love to kill KVM_ASYNC_PF_SEND_ALWAYS though, even if
>>> we do the save/restore in do_nmi(). That is some wild brain melt. Also,
>>> AFAIK none of the distros are actually shipping a PREEMPT=y kernel
>>> anyway, so killing it shouldn't matter much.
>> 
>> It will be nice if we can retain KVM_ASYNC_PF_SEND_ALWAYS. I have another
>> use case outside CONFIG_PREEMPT.
>> 
>> I am trying to extend async pf interface to also report page fault errors
>> to the guest.
> 
> Then please start over and design a sane ParaVirt Fault interface. The
> current one is utter crap.

Agreed. Donât extend the current mechanism. Replace it.

I would be happy to review a replacement. Iâm not really excited to review an extension of the current mess.  The current thing is barely, if at all, correct.