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Re: [PATCH v3 3/3] xen: don't require virtio with grants for non-PV guests

To: Juergen Gross <jgross@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, x86@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
From: Oleksandr <olekstysh@xxxxxxxxx>
Date: Wed, 22 Jun 2022 12:03:25 +0300
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Russell King <linux@xxxxxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, Viresh Kumar <viresh.kumar@xxxxxxxxxx>
Delivery-date: Wed, 22 Jun 2022 09:03:31 +0000
List-id: Xen developer discussion <xen-devel.lists.xenproject.org>


On 22.06.22 09:38, Juergen Gross wrote:

Hello Juergen

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@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V2:
- remove command line parameter (Christoph Hellwig)
V3:
- rebase to callback method



Patch looks good, just one NIT ...

---
  arch/arm/xen/enlighten.c     |  4 +++-
  arch/x86/xen/enlighten_hvm.c |  4 +++-
  arch/x86/xen/enlighten_pv.c  |  5 ++++-
  drivers/xen/Kconfig          |  9 +++++++++
  drivers/xen/grant-dma-ops.c  | 10 ++++++++++
  include/xen/xen-ops.h        |  6 ++++++
  include/xen/xen.h            |  8 --------
  7 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 1f9c3ba32833..93c8ccbf2982 100644
--- 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 8b71b1dd7639..28762f800596 100644
--- 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 e3297b15701c..5aaae8a77f55 100644
--- 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 bfd5f4f706bc..a65bd92121a5 100644
--- 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 fc0142484001..8973fc1e9ccc 100644
--- 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);
+}

... I am thinking would it be better to move this to xen/xen-ops.has grant-dma-ops.c is generic (not only for virtio, although the virtiois the first use-case)



diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
index 8973fc1..fc01424 100644
--- a/drivers/xen/grant-dma-ops.c
+++ b/drivers/xen/grant-dma-ops.c
@@ -12,8 +12,6 @@
 #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>
@@ -289,14 +287,6 @@ 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 98c399a..a9ae51b 100644
--- a/include/xen/xen-ops.h
+++ b/include/xen/xen-ops.h
@@ -6,6 +6,7 @@
 #include <linux/notifier.h>
 #include <linux/efi.h>
 #include <linux/virtio_anchor.h>
+#include <linux/virtio.h>
 #include <xen/features.h>
 #include <asm/xen/interface.h>
 #include <xen/interface/vcpu.h>
@@ -218,7 +219,13 @@ 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);
+static inline 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);
+}
 #else
 static inline void xen_grant_setup_dma_ops(struct device *dev)
 {

+
  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 80546960f8b7..98c399a960a3 100644
--- 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 +227,10 @@ static inline bool xen_is_grant_dma_device(struct device 
*dev)
  {
        return false;
  }
+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 ac5a144c6a65..a99bab817523 100644
--- 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);


--
Regards,

Oleksandr Tyshchenko

Follow-Ups:
- Re: [PATCH v3 3/3] xen: don't require virtio with grants for non-PV guests
  - From: Juergen Gross

References:
- [PATCH v3 0/3] virtio: support requiring restricted access per device
  - From: Juergen Gross
- [PATCH v3 3/3] xen: don't require virtio with grants for non-PV guests
  - From: Juergen Gross

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