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[79.178.18.124]) by smtp.gmail.com with ESMTPSA id u9sm6745769wme.16.2020.06.19.04.47.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Jun 2020 04:47:23 -0700 (PDT) Date: Fri, 19 Jun 2020 07:47:20 -0400 From: "Michael S. Tsirkin" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Cc: David Gibson , qemu-devel@nongnu.org, brijesh.singh@amd.com, pair@us.ibm.com, pbonzini@redhat.com, dgilbert@redhat.com, frankja@linux.ibm.com, Eduardo Habkost , kvm@vger.kernel.org, cohuck@redhat.com, david@redhat.com, mdroth@linux.vnet.ibm.com, pasic@linux.ibm.com, qemu-s390x@nongnu.org, qemu-ppc@nongnu.org, Richard Henderson Subject: Re: [PATCH v3 9/9] host trust limitation: Alter virtio default properties for protected guests Message-ID: <20200619074630-mutt-send-email-mst@kernel.org> References: <20200619020602.118306-1-david@gibson.dropbear.id.au> <20200619020602.118306-10-david@gibson.dropbear.id.au> <20200619101245.GC700896@redhat.com> <20200619074432-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200619074432-mutt-send-email-mst@kernel.org> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, Jun 19, 2020 at 07:46:14AM -0400, Michael S. Tsirkin wrote: > On Fri, Jun 19, 2020 at 11:12:45AM +0100, Daniel P. Berrangé wrote: > > 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 > > Agreed - my suggestion is an on/off/auto property, auto value > changes automatically, on/off is validated. In fact should we extend all bit properties to allow an auto value? > > > -- > > |: 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 :|