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Subject: Re: [PATCH v1 1/8] virtio: Force only split mode with protected guest
To:     Andi Kleen <ak@linux.intel.com>, Andy Lutomirski <luto@kernel.org>,
        mst@redhat.com
Cc:     virtualization@lists.linux-foundation.org, hch@lst.de,
        m.szyprowski@samsung.com, robin.murphy@arm.com,
        iommu@lists.linux-foundation.org, x86@kernel.org,
        sathyanarayanan.kuppuswamy@linux.intel.com, jpoimboe@redhat.com,
        linux-kernel@vger.kernel.org
References: <20210603004133.4079390-1-ak@linux.intel.com>
 <20210603004133.4079390-2-ak@linux.intel.com>
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 <a0e66b4c-cec5-2a26-9431-d5a21e22c8f2@linux.intel.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <4b071a9f-3683-b990-ddc2-450ac5a10388@redhat.com>
Date:   Fri, 4 Jun 2021 09:29:06 +0800
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在 2021/6/4 上午2:00, Andi Kleen 写道:
>
> On 6/3/2021 10:33 AM, Andy Lutomirski wrote:
>> On 6/2/21 5:41 PM, Andi Kleen wrote:
>>> Only allow split mode when in a protected guest. Followon
>>> patches harden the split mode code paths, and we don't want
>>> an malicious host to force anything else. Also disallow
>>> indirect mode for similar reasons.
>> I read this as "the virtio driver is buggy.  Let's disable most of the
>> buggy code in one special case in which we need a driver without bugs.
>> In all the other cases (e.g. hardware virtio device connected over
>> USB-C), driver bugs are still allowed."
>
> My understanding is most of the other modes (except for split with 
> separate descriptors) are obsolete and just there for compatibility. 
> As long as they're deprecated they won't harm anyone.
>
> -Andi
>

For "mode" do you packed vs split? If yes, it's not just for 
compatibility. Though packed virtqueue is designed to be more hardware 
friendly, most hardware vendors choose to start from split.

Thanks