From c731ffdf9faee74e9522dff06e61cda817902088 Mon Sep 17 00:00:00 2001 From: Halil Pasic Date: Mon, 7 Feb 2022 12:28:57 +0100 Subject: [PATCH 1/2] virtio: fix the condition for iommu_platform not supported MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit RH-Author: Dr. David Alan Gilbert RH-MergeRequest: 224: virtiofs on s390 secure execution RH-Bugzilla: 2116302 RH-Acked-by: Thomas Huth RH-Acked-by: Cornelia Huck RH-Acked-by: Cédric Le Goater RH-Commit: [1/2] d7edc7e3905a04644c9ff44b0d36122c72068e08 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 Message-Id: <20220207112857.607829-1-pasic@linux.ibm.com> Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin Acked-by: Jason Wang (cherry picked from commit e65902a913bf31ba79a83a3bd3621108b85cf645) --- 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) { + error_setg(errp, + "iommu_platform=true is not supported by the device"); + return; + } } else { vdev->dma_as = &address_space_memory; } -- 2.37.3