Re: [PATCH v8 2/2] s390: virtio: PV needs VIRTIO I/O device protection

If protected virtualization is active on s390, the virtio queues are
not accessible to the host, unless VIRTIO_F_IOMMU_PLATFORM has been
negotiated.
Define CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS and export
arch_has_restricted_memory_access to fail probe if that's
not the case, preventing a host error on access attempt.

Signed-off-by: Pierre Morel <redacted>
---
 arch/s390/Kconfig   |  1 +
 arch/s390/mm/init.c | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 9cfd8de907cb..d4a3ef4fa27b 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig

@@ -820,6 +820,7 @@ menu "Virtualization"
 config PROTECTED_VIRTUALIZATION_GUEST
 	def_bool n
 	prompt "Protected virtualization guest support"
+	select ARCH_HAS_RESTRICTED_MEMORY_ACCESS
 	help
 	  Select this option, if you want to be able to run this
 	  kernel as a protected virtualization KVM guest.

diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 6dc7c3b60ef6..aec04d7dd089 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 +162,35 @@ bool force_dma_unencrypted(struct device *dev)
 	return is_prot_virt_guest();
 }
 
+#ifdef CONFIG_ARCH_HAS_RESTRICTED_MEMORY_ACCESS
+/*
+ * arch_has_restricted_memory_access
+ * @dev: the VIRTIO device being added
+ *
+ * Return an error if required features are missing on a guest running
+ * with protected virtualization.
+ */
+int arch_has_restricted_memory_access(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");
+		return -ENODEV;
+	}
+
+	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
+		dev_warn(&dev->dev,
+			 "device must provide VIRTIO_F_IOMMU_PLATFORM\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(arch_has_restricted_memory_access);
+#endif
+
 /* protected virtualization */
 static void pv_init(void)
 {