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Subject: Re: [PATCH v1 1/8] virtio: Force only split mode with protected guest
To:     Andy Lutomirski <luto@kernel.org>, mst@redhat.com
Cc:     Jason Wang <jasowang@redhat.com>,
        virtualization@lists.linux-foundation.org, hch@lst.de,
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From:   Andi Kleen <ak@linux.intel.com>
Message-ID: <884f34e0-fcd2-bb82-9e9e-4269823fa9b2@linux.intel.com>
Date:   Thu, 3 Jun 2021 16:32:58 -0700
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> We do not need an increasing pile of kludges

Do you mean disabling features is a kludge?

If yes I disagree with that characterization.


> to make TDX and SEV “secure”.  We need the actual loaded driver to be secure.  The virtio architecture is full of legacy nonsense,
> and there is no good reason for SEV and TDX to be a giant special case.

I don't know where you see a "giant special case". Except for the 
limited feature negotiation all the changes are common, and the 
disabling of features (which is not new BTW, but already done e.g. with 
forcing DMA API in some cases) can be of course used by all these other 
technologies too. But it just cannot be done by default for everything 
because it would break compatibility. So every technology with such 
requirements has to explicitly opt-in.


>
> As I said before, real PCIe (Thunderbolt/USB-C or anything else) has the exact same problem.  The fact that TDX has encrypted memory is, at best, a poor proxy for the actual condition.  The actual condition is that the host does not trust the device to implement the virtio protocol correctly.

Right they can do similar limitations of feature sets. But again it 
cannot be default.


>
>>
>> TDX and SEV use the arch hook to enforce DMA API, so that part is also
>> solved.
>>
> Can you point me to the code you’re referring to?

See 4/8 in this patch kit. It uses an existing hook which is already 
used in tree by s390.


-Andi