Re: [PATCH] KVM: Remove redundant smp_mb() in the kvm_mmu_commit_zap_page()

[Paolo Bonzini]

On 10/03/2016 15:40, Xiao Guangrong wrote:
>      long dirty_count = kvm->tlbs_dirty;
> 
> +        /*
> +         * read tlbs_dirty before doing tlb flush to make sure not tlb
> request is
> +         * lost.
> +         */
>      smp_mb();
> +
>      if (kvm_make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH))
>          ++kvm->stat.remote_tlb_flush;
>      cmpxchg(&kvm->tlbs_dirty, dirty_count, 0);
> 
> 
> Any comment?

Compared to smp_load_acquire(), smp_mb() adds an ordering between stores
and loads.  Is the

The load of kvm->tlbs_dirty should then be

        /*
         * Read tlbs_dirty before setting KVM_REQ_TLB_FLUSH in
         * kvm_make_all_cpus_request.  This
         */
        long dirty_count = smp_load_acquire(kvm->tlbs_dirty);

Tianyu, I think Xiao provided the information that I was missing.  Would
you like to prepare the patch?

Thanks,

Paolo