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Tsirkin" , Daniel Henrique Barboza , "qemu-devel@nongnu.org" , Halil Pasic , Jakob Naucke Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Apr 27, 2022 at 8:25 PM Chenyi Qiang wrote: > > > > On 4/22/2022 3:11 PM, Chenyi Qiang wrote: > > > > > > On 2/7/2022 7:28 PM, Halil Pasic wrote: > >> The commit 04ceb61a40 ("virtio: Fail if iommu_platform is requested, but > >> unsupported") claims to fail the device hotplug when iommu_platform > >> is requested, but not supported by the (vhost) device. On the first > >> glance the condition for detecting that situation looks perfect, but > >> because a certain peculiarity of virtio_platform it ain't. > >> > >> In fact the aforementioned commit introduces a regression. It breaks > >> virtio-fs support for Secure Execution, and most likely also for AMD SEV > >> or any other confidential guest scenario that relies encrypted guest > >> memory. The same also applies to any other vhost device that does not > >> support _F_ACCESS_PLATFORM. > >> > >> The peculiarity is that iommu_platform and _F_ACCESS_PLATFORM collates > >> "device can not access all of the guest RAM" and "iova != gpa, thus > >> device needs to translate iova". > >> > >> Confidential guest technologies currently rely on the device/hypervisor > >> offering _F_ACCESS_PLATFORM, so that, after the feature has been > >> negotiated, the guest grants access to the portions of memory the > >> device needs to see. So in for confidential guests, generally, > >> _F_ACCESS_PLATFORM is about the restricted access to memory, but not > >> about the addresses used being something else than guest physical > >> addresses. > >> > >> This is the very reason for which commit f7ef7e6e3b ("vhost: correctly > >> turn on VIRTIO_F_IOMMU_PLATFORM") fences _F_ACCESS_PLATFORM from the > >> vhost device that does not need it, because on the vhost interface it > >> only means "I/O address translation is needed". > >> > >> This patch takes inspiration from f7ef7e6e3b ("vhost: correctly turn on > >> VIRTIO_F_IOMMU_PLATFORM"), and uses the same condition for detecting the > >> situation when _F_ACCESS_PLATFORM is requested, but no I/O translation > >> by the device, and thus no device capability is needed. In this > >> situation claiming that the device does not support iommu_plattform=on > >> is counter-productive. So let us stop doing that! > >> > >> Signed-off-by: Halil Pasic > >> Reported-by: Jakob Naucke > >> Fixes: 04ceb61a40 ("virtio: Fail if iommu_platform is requested, but > >> unsupported") > >> Acked-by: Cornelia Huck > >> Reviewed-by: Daniel Henrique Barboza > >> Tested-by: Daniel Henrique Barboza > >> Cc: Kevin Wolf > >> Cc: qemu-stable@nongnu.org > >> > >> --- > >> > >> v4->v5: > >> * added back the return; so if somebody were to add code to the end of > >> the function we are still good > >> v3->v4: > >> * Fixed commit message (thanks Connie) > >> * Removed counter-productive initialization (thanks Connie) > >> * Added tags > >> v2->v3: > >> * Caught a bug: I tired to check if vdev has the feature > >> ACCESS_PLATFORM after we have forced it. Moved the check > >> to a better place > >> v1->v2: > >> * Commit message tweaks. Most notably fixed commit SHA (Michael) > >> > >> --- > >> --- > >> hw/virtio/virtio-bus.c | 12 +++++++----- > >> 1 file changed, 7 insertions(+), 5 deletions(-) > >> > >> diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c > >> index d23db98c56..0f69d1c742 100644 > >> --- a/hw/virtio/virtio-bus.c > >> +++ b/hw/virtio/virtio-bus.c > >> @@ -48,6 +48,7 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, > >> Error **errp) > >> VirtioBusClass *klass = VIRTIO_BUS_GET_CLASS(bus); > >> VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev); > >> bool has_iommu = virtio_host_has_feature(vdev, > >> VIRTIO_F_IOMMU_PLATFORM); > >> + bool vdev_has_iommu; > >> Error *local_err = NULL; > >> DPRINTF("%s: plug device.\n", qbus->name); > >> @@ -69,11 +70,6 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, > >> Error **errp) > >> return; > >> } > >> - if (has_iommu && !virtio_host_has_feature(vdev, > >> VIRTIO_F_IOMMU_PLATFORM)) { > >> - error_setg(errp, "iommu_platform=true is not supported by the > >> device"); > >> - return; > >> - } > >> - > >> if (klass->device_plugged != NULL) { > >> klass->device_plugged(qbus->parent, &local_err); > >> } > >> @@ -82,9 +78,15 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, > >> Error **errp) > >> return; > >> } > >> + vdev_has_iommu = virtio_host_has_feature(vdev, > >> VIRTIO_F_IOMMU_PLATFORM); > >> if (klass->get_dma_as != NULL && has_iommu) { > >> virtio_add_feature(&vdev->host_features, > >> VIRTIO_F_IOMMU_PLATFORM); > >> vdev->dma_as = klass->get_dma_as(qbus->parent); > >> + if (!vdev_has_iommu && vdev->dma_as != &address_space_memory) { > > > > Hi Pasic, > > > > When testing the virtio-fs in Intel TDX, I met the error report in this > > check. Is it appropriate to compare the dma_as against the > > address_space_memory to detect whether the IOMMU is enabled or not? Per > > the commit ae4003738f(vhost: correctly detect the enabling IOMMU), we > > should call virtio_bus_device_iommu_enabled(vdev) instead here, correct? > > > > Sorry for bothering. > > Can virtio-fs work properly in AMD SEV? > > IIUC, If get_dma_as() is implemented and in case of PCI, > pci_get_address_space() is used and returns the bus master as. This > would fail the check here. I think the reason is that the viritio-fs is used without vIOMMU but ACCESS_PLATFORM. That's why we need to use virtio_bus_device_iommu_enabled() to allow this setup to work. Thanks > > >> + error_setg(errp, > >> + "iommu_platform=true is not supported by the > >> device"); > >> + return; > >> + } > >> } else { > >> vdev->dma_as = &address_space_memory; > >> } > >> > >> base-commit: 0d564a3e32ba8494014c67cdd2ebf0fb71860dff > > >