linux-kernel - Re: [PATCH v3 8/8] KVM: x86/mmu: Lazily allocate memslot rmaps

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Date:   Fri, 7 May 2021 10:28:11 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Kai Huang <kai.huang@...el.com>,
        Keqian Zhu <zhukeqian1@...wei.com>
Subject: Re: [PATCH v3 8/8] KVM: x86/mmu: Lazily allocate memslot rmaps

On 06/05/21 20:42, Ben Gardon wrote:
> +	/*
> +	 * memslots_have_rmaps is set and read in different lock contexts,
> +	 * so protect it with smp_load/store.
> +	 */
> +	smp_store_release(&kvm->arch.memslots_have_rmaps, true);

Shorter and better: /* write rmap pointers before memslots_have_rmaps */

> +	mutex_unlock(&kvm->slots_arch_lock);
> +	return 0;
> +}
> +
>   bool kvm_memslots_have_rmaps(struct kvm *kvm)
>   {
> -	return kvm->arch.memslots_have_rmaps;
> +	/*
> +	 * memslots_have_rmaps is set and read in different lock contexts,
> +	 * so protect it with smp_load/store.
> +	 */
> +	return smp_load_acquire(&kvm->arch.memslots_have_rmaps);
>   }
>   

Likewise, /* read memslots_have_rmaps before the rmaps themselves */

Paolo