linux-kernel - Re: [PATCH] KVM: Remove duplicated zero clear with dirty

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Message-ID: <e4d78c69-c723-758e-374c-514088d8f961@loongson.cn>
Date: Fri, 21 Jun 2024 09:59:49 +0800
From: maobibo <maobibo@...ngson.cn>
To: Paolo Bonzini <pbonzini@...hat.com>,
 Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: Remove duplicated zero clear with dirty_bitmap
 buffer



On 2024/6/21 上午5:17, Paolo Bonzini wrote:
> On 6/14/24 04:45, maobibo wrote:
>> I do not know whether KVM_DIRTY_LOG_INITIALLY_SET should be enabled on 
>> LoongArch. If it is set, write protection for second MMU will start 
>> one by one in function kvm_arch_mmu_enable_log_dirty_pt_masked() when 
>> dirty log is cleared if it is set, else write protection will start in 
>> function kvm_arch_commit_memory_region() when flag of memslot is changed.
>>
>> I do not see the obvious benefits between these two write protect 
>> stages. Can anyone give me any hints?
> 
> The advantage is that you get (a lot) fewer vmexits to set the dirty 
> bitmap, and that write protection is not done in a single expensive 
> step.  Instead it is done at the time that userspace first clears the 
> bits in the dirty bitmap.  It provides much better performance.
Got it, thanks for the explanation .

Regards
Bibo Mao
> 
> Paolo
>