Re: [PATCH] kvm: x86: mmu: Always flush TLBs when enabling dirty logging

[Junaid Shahid <junaids@google.com>]

On 7/25/22 15:32, Sean Christopherson wrote:
> ...
> 
> If we go the "always flush" route, I would word the comment to explicitly call out
> that the alternative would be to check if the SPTE is MMU-writable.
> 
> But my preference would actually be to keep the conditional flushing.  Not because
> I think it will provide better performance (probably the opposite if anything),
> but because it documents the dependencies/rules in code, and because "always flush"
> reads like it's working around a KVM bug.  It's not a super strong preference though.
> 
> Partially, I think it'd be this?
> 

This would work, but I am slightly leaning away from it because it could 
increase CPU overhead in some cases. If you don't have a strong preference for 
it, then I think we could just do an unconditional flush with a more detailed 
comment explaining the interaction with clear_young() as well as the alternative 
of checking the MMU-writable bit.

Thanks,
Junaid