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[109.64.41.91]) by smtp.gmail.com with ESMTPSA id t189sm16775933wma.4.2020.06.06.13.21.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 06 Jun 2020 13:21:34 -0700 (PDT) Date: Sat, 6 Jun 2020 16:21:31 -0400 From: "Michael S. Tsirkin" To: David Gibson Cc: qemu-devel@nongnu.org, brijesh.singh@amd.com, frankja@linux.ibm.com, dgilbert@redhat.com, pair@us.ibm.com, qemu-ppc@nongnu.org, kvm@vger.kernel.org, mdroth@linux.vnet.ibm.com, cohuck@redhat.com, Marcel Apfelbaum , Paolo Bonzini , Richard Henderson , Eduardo Habkost Subject: Re: [RFC v2 18/18] guest memory protection: Alter virtio default properties for protected guests Message-ID: <20200606162014-mutt-send-email-mst@kernel.org> References: <20200521034304.340040-1-david@gibson.dropbear.id.au> <20200521034304.340040-19-david@gibson.dropbear.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200521034304.340040-19-david@gibson.dropbear.id.au> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, May 21, 2020 at 01:43:04PM +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 guest memory protection 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 88d699bceb..cb6580954e 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/guest-memory-protection.h" > +#include "hw/virtio/virtio.h" > +#include "hw/virtio/virtio-pci.h" > > GlobalProperty hw_compat_5_0[] = {}; > const size_t hw_compat_5_0_len = G_N_ELEMENTS(hw_compat_5_0); > @@ -1159,6 +1161,15 @@ 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"); > } > I think it's a reasonable way to address this overall. As Cornelia has commented, addressing ccw as well as cases where user has specified the property manually could be worth-while. > machine_class->init(machine); > -- > 2.26.2