xen: don't require virtio with grants for non-PV guests

Commit fa1f57421e0b ("xen/virtio: Enable restricted memory access using
Xen grant mappings") introduced a new requirement for using virtio
devices: the backend now needs to support the VIRTIO_F_ACCESS_PLATFORM
feature.

This is an undue requirement for non-PV guests, as those can be operated
with existing backends without any problem, as long as those backends
are running in dom0.

Per default allow virtio devices without grant support for non-PV
guests.

On Arm require VIRTIO_F_ACCESS_PLATFORM for devices having been listed
in the device tree to use grants.

Add a new config item to always force use of grants for virtio.

Fixes: fa1f57421e0b ("xen/virtio: Enable restricted memory access using Xen grant mappings")
Reported-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.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/20220622063838.8854-4-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 1f9c3ba..93c8ccb 100644 (file)
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -34,6 +34,7 @@
 #include <linux/timekeeping.h>
 #include <linux/timekeeper_internal.h>
 #include <linux/acpi.h>
+#include <linux/virtio_anchor.h>
 
 #include <linux/mm.h>
 
@@ -443,7 +444,8 @@ static int __init xen_guest_init(void)
        if (!xen_domain())
                return 0;
 
-       xen_set_restricted_virtio_memory_access();
+       if (IS_ENABLED(CONFIG_XEN_VIRTIO))
+               virtio_set_mem_acc_cb(xen_virtio_mem_acc);
 
        if (!acpi_disabled)
                xen_acpi_guest_init();

diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index 8b71b1d..28762f8 100644 (file)
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -4,6 +4,7 @@
 #include <linux/cpu.h>
 #include <linux/kexec.h>
 #include <linux/memblock.h>
+#include <linux/virtio_anchor.h>
 
 #include <xen/features.h>
 #include <xen/events.h>
@@ -195,7 +196,8 @@ static void __init xen_hvm_guest_init(void)
        if (xen_pv_domain())
                return;
 
-       xen_set_restricted_virtio_memory_access();
+       if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT))
+               virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc);
 
        init_hvm_pv_info();
 

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 70fb2ea..0ed2e48 100644 (file)
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -31,6 +31,7 @@
 #include <linux/gfp.h>
 #include <linux/edd.h>
 #include <linux/reboot.h>
+#include <linux/virtio_anchor.h>
 
 #include <xen/xen.h>
 #include <xen/events.h>
@@ -109,7 +110,9 @@ static DEFINE_PER_CPU(struct tls_descs, shadow_tls_desc);
 
 static void __init xen_pv_init_platform(void)
 {
-       xen_set_restricted_virtio_memory_access();
+       /* PV guests can't operate virtio devices without grants. */
+       if (IS_ENABLED(CONFIG_XEN_VIRTIO))
+               virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc);
 
        populate_extra_pte(fix_to_virt(FIX_PARAVIRT_BOOTMAP));
 

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index bfd5f4f..a65bd92 100644 (file)
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -355,4 +355,13 @@ config XEN_VIRTIO
 
          If in doubt, say n.
 
+config XEN_VIRTIO_FORCE_GRANT
+       bool "Require Xen virtio support to use grants"
+       depends on XEN_VIRTIO
+       help
+         Require virtio for Xen guests to use grant mappings.
+         This will avoid the need to give the backend the right to map all
+         of the guest memory. This will need support on the backend side
+         (e.g. qemu or kernel, depending on the virtio device types used).
+
 endmenu

diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
index fc01424..8973fc1 100644 (file)
--- a/drivers/xen/grant-dma-ops.c
+++ b/drivers/xen/grant-dma-ops.c
@@ -12,6 +12,8 @@
 #include <linux/of.h>
 #include <linux/pfn.h>
 #include <linux/xarray.h>
+#include <linux/virtio_anchor.h>
+#include <linux/virtio.h>
 #include <xen/xen.h>
 #include <xen/xen-ops.h>
 #include <xen/grant_table.h>
@@ -287,6 +289,14 @@ bool xen_is_grant_dma_device(struct device *dev)
        return has_iommu;
 }
 
+bool xen_virtio_mem_acc(struct virtio_device *dev)
+{
+       if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT))
+               return true;
+
+       return xen_is_grant_dma_device(dev->dev.parent);
+}
+
 void xen_grant_setup_dma_ops(struct device *dev)
 {
        struct xen_grant_dma_data *data;

diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
index 8054696..dae0f35 100644 (file)
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -5,6 +5,7 @@
 #include <linux/percpu.h>
 #include <linux/notifier.h>
 #include <linux/efi.h>
+#include <linux/virtio_anchor.h>
 #include <xen/features.h>
 #include <asm/xen/interface.h>
 #include <xen/interface/vcpu.h>
@@ -217,6 +218,7 @@ static inline void xen_preemptible_hcall_end(void) { }
 #ifdef CONFIG_XEN_GRANT_DMA_OPS
 void xen_grant_setup_dma_ops(struct device *dev);
 bool xen_is_grant_dma_device(struct device *dev);
+bool xen_virtio_mem_acc(struct virtio_device *dev);
 #else
 static inline void xen_grant_setup_dma_ops(struct device *dev)
 {
@@ -225,6 +227,13 @@ static inline bool xen_is_grant_dma_device(struct device *dev)
 {
        return false;
 }
+
+struct virtio_device;
+
+static inline bool xen_virtio_mem_acc(struct virtio_device *dev)
+{
+       return false;
+}
 #endif /* CONFIG_XEN_GRANT_DMA_OPS */
 
 #endif /* INCLUDE_XEN_OPS_H */

diff --git a/include/xen/xen.h b/include/xen/xen.h
index ac5a144..a99bab8 100644 (file)
--- a/include/xen/xen.h
+++ b/include/xen/xen.h
@@ -52,14 +52,6 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
 extern u64 xen_saved_max_mem_size;
 #endif
 
-#include <linux/virtio_anchor.h>
-
-static inline void xen_set_restricted_virtio_memory_access(void)
-{
-       if (IS_ENABLED(CONFIG_XEN_VIRTIO) && xen_domain())
-               virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc);
-}
-
 #ifdef CONFIG_XEN_UNPOPULATED_ALLOC
 int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages);
 void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages);