netdev - Re: [PATCH 2/2] vhost: re-introducing metadata acceleration through kernel virtual address

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Date:   Mon, 9 Sep 2019 15:23:58 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        jgg@...lanox.com, aarcange@...hat.com, jglisse@...hat.com,
        linux-mm@...ck.org,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Christoph Hellwig <hch@...radead.org>,
        David Miller <davem@...emloft.net>,
        linux-arm-kernel@...ts.infradead.org, linux-parisc@...r.kernel.org
Subject: Re: [PATCH 2/2] vhost: re-introducing metadata acceleration through
 kernel virtual address


On 2019/9/9 下午12:45, Michael S. Tsirkin wrote:
>>> Since idx can be speculated, I guess we need array_index_nospec here?
>> So we have
>>
>> ACQUIRE(mmu_lock)
>>
>> get idx
>>
>> RELEASE(mmu_lock)
>>
>> ACQUIRE(mmu_lock)
>>
>> read array[idx]
>>
>> RELEASE(mmu_lock)
>>
>> Then I think idx can't be speculated consider we've passed RELEASE +
>> ACQUIRE?
> I don't think memory barriers have anything to do with speculation,
> they are architectural.
>

Oh right. Let me add array_index_nospec() in next version.

Thanks