Re: [PATCH] KVM: Remove duplicated zero clear with dirty_bitmap buffer

[maobibo]

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