Re: [PATCH] KVM: x86/MMU: Zap non-leaf SPTEs when disabling dirty logging

[Paolo Bonzini <pbonzini@redhat.com>]

On 5/26/22 16:30, Peter Xu wrote:
> On Thu, May 26, 2022 at 02:01:43PM +0200, Paolo Bonzini wrote:
>> On 5/26/22 01:09, Ben Gardon wrote:
>>> +		WARN_ON(max_mapping_level < iter.level);
>>> +
>>> +		/*
>>> +		 * If this page is already mapped at the highest
>>> +		 * viable level, there's nothing more to do.
>>> +		 */
>>> +		if (max_mapping_level == iter.level)
>>> +			continue;
>>> +
>>> +		/*
>>> +		 * The page can be remapped at a higher level, so step
>>> +		 * up to zap the parent SPTE.
>>> +		 */
>>> +		while (max_mapping_level > iter.level)
>>> +			tdp_iter_step_up(&iter);
>>> +
>>>    		/* Note, a successful atomic zap also does a remote TLB flush. */
>>> -		if (tdp_mmu_zap_spte_atomic(kvm, &iter))
>>> -			goto retry;
>>> +		tdp_mmu_zap_spte_atomic(kvm, &iter);
>>> +
>>
>> Can you make this a sparate function (for example
>> tdp_mmu_zap_collapsible_spte_atomic)?  Otherwise looks great!
> 
> There could be a tiny downside of using a helper in that it'll hide the
> step-up of the iterator, which might not be as obvious as keeping it in the
> loop?

That's true, my reasoning is that zapping at a higher level can only be 
done by first moving the iterator up.  Maybe 
tdp_mmu_zap_at_level_atomic() is a better Though, I can very well apply 
this patch as is.

Paolo