Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
References: <20190323165456-mutt-send-email-mst@kernel.org> <87a7go71hz.fsf@morokweng.localdomain> <20190520090939-mutt-send-email-mst@kernel.org> <877ea26tk8.fsf@morokweng.localdomain> <20190603211528-mutt-send-email-mst@kernel.org> <877e96qxm7.fsf@morokweng.localdomain> <20190701092212-mutt-send-email-mst@kernel.org> <87d0id9nah.fsf@morokweng.localdomain> <20190715103411-mutt-send-email-mst@kernel.org> <874l3nnist.fsf@morokweng.localdomain> <20190715163453-mutt-send-email-mst@kernel.org>
User-agent: mu4e 1.2.0; emacs 26.2
From:   Thiago Jung Bauermann <bauerman@linux.ibm.com>
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     virtualization@lists.linux-foundation.org,
        linuxppc-dev@lists.ozlabs.org, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, Jason Wang <jasowang@redhat.com>,
        Christoph Hellwig <hch@lst.de>,
        David Gibson <david@gibson.dropbear.id.au>,
        Alexey Kardashevskiy <aik@linux.ibm.com>,
        Paul Mackerras <paulus@ozlabs.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Ram Pai <linuxram@us.ibm.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@arm.com>,
        Michael Roth <mdroth@linux.vnet.ibm.com>,
        Mike Anderson <andmike@linux.ibm.com>
Subject: Re: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted
In-reply-to: <20190715163453-mutt-send-email-mst@kernel.org>
Date:   Mon, 15 Jul 2019 19:03:03 -0300
Message-ID: <8736j7neg8.fsf@morokweng.localdomain>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


Michael S. Tsirkin <mst@redhat.com> writes:

> On Mon, Jul 15, 2019 at 05:29:06PM -0300, Thiago Jung Bauermann wrote:
>>
>> Michael S. Tsirkin <mst@redhat.com> writes:
>>
>> > On Sun, Jul 14, 2019 at 02:51:18AM -0300, Thiago Jung Bauermann wrote:
>> >>
>> >>
>> >> Michael S. Tsirkin <mst@redhat.com> writes:
>> >>
>> >> > So this is what I would call this option:
>> >> >
>> >> > VIRTIO_F_ACCESS_PLATFORM_IDENTITY_ADDRESS
>> >> >
>> >> > and the explanation should state that all device
>> >> > addresses are translated by the platform to identical
>> >> > addresses.
>> >> >
>> >> > In fact this option then becomes more, not less restrictive
>> >> > than VIRTIO_F_ACCESS_PLATFORM - it's a promise
>> >> > by guest to only create identity mappings,
>> >> > and only before driver_ok is set.
>> >> > This option then would always be negotiated together with
>> >> > VIRTIO_F_ACCESS_PLATFORM.
>> >> >
>> >> > Host then must verify that
>> >> > 1. full 1:1 mappings are created before driver_ok
>> >> >     or can we make sure this happens before features_ok?
>> >> >     that would be ideal as we could require that features_ok fails
>> >> > 2. mappings are not modified between driver_ok and reset
>> >> >     i guess attempts to change them will fail -
>> >> >     possibly by causing a guest crash
>> >> >     or some other kind of platform-specific error
>> >>
>> >> I think VIRTIO_F_ACCESS_PLATFORM_IDENTITY_ADDRESS is good, but requiring
>> >> it to be accompanied by ACCESS_PLATFORM can be a problem. One reason is
>> >> SLOF as I mentioned above, another is that we would be requiring all
>> >> guests running on the machine (secure guests or not, since we would use
>> >> the same configuration for all guests) to support it. But
>> >> ACCESS_PLATFORM is relatively recent so it's a bit early for that. For
>> >> instance, Ubuntu 16.04 LTS (which is still supported) doesn't know about
>> >> it and wouldn't be able to use the device.
>> >
>> > OK and your target is to enable use with kernel drivers within
>> > guests, right?
>>
>> Right.
>>
>> > My question is, we are defining a new flag here, I guess old guests
>> > then do not set it. How does it help old guests? Or maybe it's
>> > not designed to ...
>>
>> Indeed. The idea is that QEMU can offer the flag, old guests can reject
>> it (or even new guests can reject it, if they decide not to convert into
>> secure VMs) and the feature negotiation will succeed with the flag
>> unset.
>
> OK. And then what does QEMU do? Assume guest is not encrypted I guess?

There's nothing different that QEMU needs to do, with or without the
flag. the perspective of the host, a secure guest and a regular guest
work the same way with respect to virtio.

--
Thiago Jung Bauermann
IBM Linux Technology Center