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Fri, 19 Jun 2020 10:12:48 +0000 (UTC) Date: Fri, 19 Jun 2020 11:12:45 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: David Gibson Subject: Re: [PATCH v3 9/9] host trust limitation: Alter virtio default properties for protected guests Message-ID: <20200619101245.GC700896@redhat.com> References: <20200619020602.118306-1-david@gibson.dropbear.id.au> <20200619020602.118306-10-david@gibson.dropbear.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200619020602.118306-10-david@gibson.dropbear.id.au> User-Agent: Mutt/1.14.0 (2020-05-02) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Received-SPF: pass client-ip=207.211.31.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/19 03:15:03 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: pair@us.ibm.com, brijesh.singh@amd.com, frankja@linux.ibm.com, kvm@vger.kernel.org, mst@redhat.com, cohuck@redhat.com, david@redhat.com, qemu-devel@nongnu.org, dgilbert@redhat.com, pasic@linux.ibm.com, qemu-s390x@nongnu.org, qemu-ppc@nongnu.org, pbonzini@redhat.com, Richard Henderson , mdroth@linux.vnet.ibm.com, Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Jun 19, 2020 at 12:06:02PM +1000, David Gibson wrote: > The default behaviour for virtio devices is not to use the platforms normal > DMA paths, but instead to use the fact that it's running in a hypervisor > to directly access guest memory. That doesn't work if the guest's memory > is protected from hypervisor access, such as with AMD's SEV or POWER's PEF. > > So, if a host trust limitation mechanism is enabled, then apply the > iommu_platform=on option so it will go through normal DMA mechanisms. > Those will presumably have some way of marking memory as shared with the > hypervisor or hardware so that DMA will work. > > Signed-off-by: David Gibson > --- > hw/core/machine.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/hw/core/machine.c b/hw/core/machine.c > index a71792bc16..8dfc1bb3f8 100644 > --- a/hw/core/machine.c > +++ b/hw/core/machine.c > @@ -28,6 +28,8 @@ > #include "hw/mem/nvdimm.h" > #include "migration/vmstate.h" > #include "exec/host-trust-limitation.h" > +#include "hw/virtio/virtio.h" > +#include "hw/virtio/virtio-pci.h" > > GlobalProperty hw_compat_5_0[] = { > { "virtio-balloon-device", "page-poison", "false" }, > @@ -1165,6 +1167,15 @@ void machine_run_board_init(MachineState *machine) > * areas. > */ > machine_set_mem_merge(OBJECT(machine), false, &error_abort); > + > + /* > + * Virtio devices can't count on directly accessing guest > + * memory, so they need iommu_platform=on to use normal DMA > + * mechanisms. That requires disabling legacy virtio support > + * for virtio pci devices > + */ > + object_register_sugar_prop(TYPE_VIRTIO_PCI, "disable-legacy", "on"); > + object_register_sugar_prop(TYPE_VIRTIO_DEVICE, "iommu_platform", "on"); > } Silently changing the user's request configuration like this is a bad idea. The "disable-legacy" option in particular is undesirable as that switches the device to virtio-1.0 only mode, which exposes a different PCI ID to the guest. If some options are incompatible with encryption, then we should raise a fatal error at startup, so applications/admins are aware that their requested config is broken. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|