Re: [PATCH v5 2/2] s390: virtio: PV needs VIRTIO I/O device protection

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On 2020-07-09 11:55, Halil Pasic wrote:
On Thu, 9 Jul 2020 10:57:33 +0200
Cornelia Huck <cohuck@xxxxxxxxxx> wrote:

On Thu,  9 Jul 2020 10:39:19 +0200
Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:

If protected virtualization is active on s390, the virtio queues are
not accessible to the host, unless VIRTIO_F_IOMMU_PLATFORM has been
negotiated. Use the new arch_validate_virtio_features() interface to
fail probe if that's not the case, preventing a host error on access
attempt

Punctuation at the end?

Also 'that's not the case' refers to the negation
'VIRTIO_F_IOMMU_PLATFORM has been negotiated',
arch_validate_virtio_features() is however part of
virtio_finalize_features(), which is in turn part of the feature
negotiation. But that is details. I'm fine with keeping the message as
is.


Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
---
  arch/s390/mm/init.c | 27 +++++++++++++++++++++++++++
  1 file changed, 27 insertions(+)

diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 6dc7c3b60ef6..b8e6f90117da 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_config.h>
pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir); @@ -161,6 +162,32 @@ bool force_dma_unencrypted(struct device *dev)
  	return is_prot_virt_guest();
  }
+/*
+ * arch_validate_virtio_features
+ * @dev: the VIRTIO device being added
+ *
+ * Return an error if required features are missing on a guest running
+ * with protected virtualization.
+ */
+int arch_validate_virtio_features(struct virtio_device *dev)
+{
+	if (!is_prot_virt_guest())
+		return 0;
+
+	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
+		dev_warn(&dev->dev, "device must provide VIRTIO_F_VERSION_1\n");

I'd probably use "legacy virtio not supported with protected
virtualization".

+		return -ENODEV;
+	}
+
+	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
+		dev_warn(&dev->dev,
+			 "device must provide VIRTIO_F_IOMMU_PLATFORM\n");

"support for limited memory access required for protected
virtualization"

?

Mentioning the feature flag is shorter in both cases, though.

I liked the messages in v4. Why did we change those? Did somebody
complain?

I prefer the old ones, but it any case:

Acked-by: Halil Pasic <pasic@xxxxxxxxxxxxx>

Thanks,
Pierre


--
Pierre Morel
IBM Lab Boeblingen
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