linux-kernel - Re: [PATCH v4 4/6] KVM: MMU: fast invalid all shadow pages

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Message-ID: <51835087.8090605@linux.vnet.ibm.com>
Date:	Fri, 03 May 2013 13:52:07 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	gleb@...hat.com, avi.kivity@...il.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	takuya.yoshikawa@...il.com
Subject: Re: [PATCH v4 4/6] KVM: MMU: fast invalid all shadow pages

On 05/03/2013 09:05 AM, Marcelo Tosatti wrote:

>> +
>> +/*
>> + * Fast invalid all shadow pages belong to @slot.
>> + *
>> + * @slot != NULL means the invalidation is caused the memslot specified
>> + * by @slot is being deleted, in this case, we should ensure that rmap
>> + * and lpage-info of the @slot can not be used after calling the function.
>> + *
>> + * @slot == NULL means the invalidation due to other reasons, we need
>> + * not care rmap and lpage-info since they are still valid after calling
>> + * the function.
>> + */
>> +void kvm_mmu_invalid_memslot_pages(struct kvm *kvm,
>> +				   struct kvm_memory_slot *slot)
>> +{
>> +	spin_lock(&kvm->mmu_lock);
>> +	kvm->arch.mmu_valid_gen++;
>> +
>> +	/*
>> +	 * All shadow paes are invalid, reset the large page info,
>> +	 * then we can safely desotry the memslot, it is also good
>> +	 * for large page used.
>> +	 */
>> +	kvm_clear_all_lpage_info(kvm);
> 
> Xiao,
> 
> I understood it was agreed that simple mmu_lock lockbreak while
> avoiding zapping of newly instantiated pages upon a
> 
> 	if(spin_needbreak)
> 		cond_resched_lock()
> 
> cycle was enough as a first step? And then later introduce root zapping
> along with measurements.
> 
> https://lkml.org/lkml/2013/4/22/544

Yes, it is.

See the changelog in 0/0:

" we use lock-break technique to zap all sptes linked on the
invalid rmap, it is not very effective but good for the first step."

Thanks!


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