virtio: replace restricted mem access flag with callback

Instead of having a global flag to require restricted memory access
for all virtio devices, introduce a callback which can select that
requirement on a per-device basis.

For convenience add a common function returning always true, which can
be used for use cases like SEV.

Per default use a callback always returning false.

As the callback needs to be set in early init code already, add a
virtio anchor which is builtin in case virtio is enabled.

Signed-off-by: Juergen Gross <jgross@suse.com>
Tested-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> # Arm64 guest using Xen
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Link: https://lore.kernel.org/r/20220622063838.8854-2-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>

arch/s390/mm/init.c

@@ -31,7 +31,6 @@
 #include <linux/cma.h>
 #include <linux/gfp.h>
 #include <linux/dma-direct.h>
-#include <linux/platform-feature.h>
 #include <asm/processor.h>
 #include <linux/uaccess.h>
 #include <asm/pgalloc.h>
@@ -48,6 +47,7 @@
 #include <asm/kasan.h>
 #include <asm/dma-mapping.h>
 #include <asm/uv.h>
+#include <linux/virtio_anchor.h>
 #include <linux/virtio_config.h>
 
 pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(".bss..swapper_pg_dir");
@@ -175,7 +175,7 @@ static void pv_init(void)
 	if (!is_prot_virt_guest())
 		return;
 
-	platform_set(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
+	virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc);
 
 	/* make sure bounce buffers are shared */
 	swiotlb_init(true, SWIOTLB_FORCE | SWIOTLB_VERBOSE);

arch/x86/mm/mem_encrypt_amd.c

@@ -20,8 +20,8 @@
 #include <linux/bitops.h>
 #include <linux/dma-mapping.h>
 #include <linux/virtio_config.h>
+#include <linux/virtio_anchor.h>
 #include <linux/cc_platform.h>
-#include <linux/platform-feature.h>
 
 #include <asm/tlbflush.h>
 #include <asm/fixmap.h>
@@ -245,7 +245,7 @@ void __init sev_setup_arch(void)
 	swiotlb_adjust_size(size);
 
 	/* Set restricted memory access for virtio. */
-	platform_set(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
+	virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc);
 }
 
 static unsigned long pg_level_to_pfn(int level, pte_t *kpte, pgprot_t *ret_prot)

drivers/virtio/Kconfig

@@ -1,6 +1,10 @@
 # SPDX-License-Identifier: GPL-2.0-only
+config VIRTIO_ANCHOR
+	bool
+
 config VIRTIO
 	tristate
+	select VIRTIO_ANCHOR
 	help
 	  This option is selected by any driver which implements the virtio
 	  bus, such as CONFIG_VIRTIO_PCI, CONFIG_VIRTIO_MMIO, CONFIG_RPMSG

drivers/virtio/Makefile

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_VIRTIO) += virtio.o virtio_ring.o
+obj-$(CONFIG_VIRTIO_ANCHOR) += virtio_anchor.o
 obj-$(CONFIG_VIRTIO_PCI_LIB) += virtio_pci_modern_dev.o
 obj-$(CONFIG_VIRTIO_PCI_LIB_LEGACY) += virtio_pci_legacy_dev.o
 obj-$(CONFIG_VIRTIO_MMIO) += virtio_mmio.o

drivers/virtio/virtio.c

@@ -2,10 +2,10 @@
 #include <linux/virtio.h>
 #include <linux/spinlock.h>
 #include <linux/virtio_config.h>
+#include <linux/virtio_anchor.h>
 #include <linux/module.h>
 #include <linux/idr.h>
 #include <linux/of.h>
-#include <linux/platform-feature.h>
 #include <uapi/linux/virtio_ids.h>
 
 /* Unique numbering for virtio devices. */
@@ -174,7 +174,7 @@ static int virtio_features_ok(struct virtio_device *dev)
 
 	might_sleep();
 
-	if (platform_has(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS)) {
+	if (virtio_check_mem_acc_cb(dev)) {
 		if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
 			dev_warn(&dev->dev,
 				 "device must provide VIRTIO_F_VERSION_1\n");

drivers/virtio/virtio_anchor.c

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/virtio.h>
+#include <linux/virtio_anchor.h>
+
+bool virtio_require_restricted_mem_acc(struct virtio_device *dev)
+{
+	return true;
+}
+EXPORT_SYMBOL_GPL(virtio_require_restricted_mem_acc);
+
+static bool virtio_no_restricted_mem_acc(struct virtio_device *dev)
+{
+	return false;
+}
+
+bool (*virtio_check_mem_acc_cb)(struct virtio_device *dev) =
+	virtio_no_restricted_mem_acc;
+EXPORT_SYMBOL_GPL(virtio_check_mem_acc_cb);

include/linux/platform-feature.h

@@ -6,11 +6,7 @@
 #include <asm/platform-feature.h>
 
 /* The platform features are starting with the architecture specific ones. */
-
-/* Used to enable platform specific DMA handling for virtio devices. */
-#define PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS	(0 + PLATFORM_ARCH_FEAT_N)
-
-#define PLATFORM_FEAT_N				(1 + PLATFORM_ARCH_FEAT_N)
+#define PLATFORM_FEAT_N				(0 + PLATFORM_ARCH_FEAT_N)
 
 void platform_set(unsigned int feature);
 void platform_clear(unsigned int feature);

include/linux/virtio_anchor.h

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_VIRTIO_ANCHOR_H
+#define _LINUX_VIRTIO_ANCHOR_H
+
+#ifdef CONFIG_VIRTIO_ANCHOR
+struct virtio_device;
+
+bool virtio_require_restricted_mem_acc(struct virtio_device *dev);
+extern bool (*virtio_check_mem_acc_cb)(struct virtio_device *dev);
+
+static inline void virtio_set_mem_acc_cb(bool (*func)(struct virtio_device *))
+{
+	virtio_check_mem_acc_cb = func;
+}
+#else
+#define virtio_set_mem_acc_cb(func) do { } while (0)
+#endif
+
+#endif /* _LINUX_VIRTIO_ANCHOR_H */

include/xen/xen.h

@@ -52,12 +52,12 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
 extern u64 xen_saved_max_mem_size;
 #endif
 
-#include <linux/platform-feature.h>
+#include <linux/virtio_anchor.h>
 
 static inline void xen_set_restricted_virtio_memory_access(void)
 {
 	if (IS_ENABLED(CONFIG_XEN_VIRTIO) && xen_domain())
-		platform_set(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
+		virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc);
 }
 
 #ifdef CONFIG_XEN_UNPOPULATED_ALLOC