On Thu, Apr 28, 2022 at 12:57 PM Michael S. Tsirkin <m...@redhat.com> wrote: > > On Thu, Apr 28, 2022 at 11:01:10AM +0800, Jason Wang wrote: > > On Wed, Apr 27, 2022 at 8:25 PM Chenyi Qiang <chenyi.qi...@intel.com> 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 <pa...@linux.ibm.com> > > > >> Reported-by: Jakob Naucke <jakob.nau...@ibm.com> > > > >> Fixes: 04ceb61a40 ("virtio: Fail if iommu_platform is requested, but > > > >> unsupported") > > > >> Acked-by: Cornelia Huck <coh...@redhat.com> > > > >> Reviewed-by: Daniel Henrique Barboza <danielhb...@gmail.com> > > > >> Tested-by: Daniel Henrique Barboza <danielhb...@gmail.com> > > > >> Cc: Kevin Wolf <kw...@redhat.com> > > > >> Cc: qemu-sta...@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 > > Do you retract your ack then?
Somehow, we need a fix on top. Thanks > > > > > > > >> + error_setg(errp, > > > >> + "iommu_platform=true is not supported by the > > > >> device"); > > > >> + return; > > > >> + } > > > >> } else { > > > >> vdev->dma_as = &address_space_memory; > > > >> } > > > >> > > > >> base-commit: 0d564a3e32ba8494014c67cdd2ebf0fb71860dff > > > > > > > >