Re: [PATCH v3 1/1] s390: virtio: let arch accept devices without IOMMU feature

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On 2020-06-17 15:36, Tom Lendacky wrote:
On 6/17/20 5:43 AM, Pierre Morel wrote:
An architecture protecting the guest memory against unauthorized host
access may want to enforce VIRTIO I/O device protection through the
use of VIRTIO_F_IOMMU_PLATFORM.

Let's give a chance to the architecture to accept or not devices
without VIRTIO_F_IOMMU_PLATFORM.

Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
  arch/s390/mm/init.c     |  6 ++++++
  drivers/virtio/virtio.c | 22 ++++++++++++++++++++++
  include/linux/virtio.h  |  2 ++
  3 files changed, 30 insertions(+)

diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 6dc7c3b60ef6..215070c03226 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -45,6 +45,7 @@
  #include <asm/kasan.h>
  #include <asm/dma-mapping.h>
  #include <asm/uv.h>
+#include <linux/virtio.h>
pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir); @@ -161,6 +162,11 @@ bool force_dma_unencrypted(struct device *dev)
  	return is_prot_virt_guest();
  }
+int arch_needs_virtio_iommu_platform(struct virtio_device *dev)
+{
+	return is_prot_virt_guest();
+}
+
  /* protected virtualization */
  static void pv_init(void)
  {
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index a977e32a88f2..aa8e01104f86 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -167,6 +167,21 @@ void virtio_add_status(struct virtio_device *dev, unsigned int status)
  }
  EXPORT_SYMBOL_GPL(virtio_add_status);
+/*
+ * arch_needs_virtio_iommu_platform - provide arch specific hook when finalizing
+ *				      features for VIRTIO device dev
+ * @dev: the VIRTIO device being added
+ *
+ * Permits the platform to provide architecture specific functionality when
+ * devices features are finalized. This is the default implementation.
+ * Architecture implementations can override this.
+ */
+
+int __weak arch_needs_virtio_iommu_platform(struct virtio_device *dev)
+{
+	return 0;
+}
+
  int virtio_finalize_features(struct virtio_device *dev)
  {
  	int ret = dev->config->finalize_features(dev);
@@ -179,6 +194,13 @@ int virtio_finalize_features(struct virtio_device *dev)
  	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
  		return 0;
+ if (arch_needs_virtio_iommu_platform(dev) &&
+		!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {

Just a style nit, but the "!virtio..." should be directly under the
"arch_...", not tabbed out.

Oh right, thanks!

Pierre


Thanks,
Tom


...snip...

--
Pierre Morel
IBM Lab Boeblingen
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