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Re: [PATCH V4 23/24] libxl: Introduce basic virtio-mmio support on Arm

On 15.01.21 23:30, Julien Grall wrote:
Hi Oleksandr,

Hi Julien

On 12/01/2021 21:52, Oleksandr Tyshchenko wrote:
From: Julien Grall <julien.grall@xxxxxxx>

This patch creates specific device node in the Guest device-tree
with allocated MMIO range and SPI interrupt if specific 'virtio'
property is present in domain config.

From my understanding, for each virtio device use the MMIO transparent,
we would need to reserve an area in memory for its exclusive use.

If I were an admin, I would expect to only describe the list of virtio devices I want to assign to my guest and then let the toolstack figure out how to expose them.

Yes, I think in the same way.

So I am not quite too sure how this new parameter can be used. Could you expand it?
The original idea was to set it if we are going to assign virtio device(s) to the guest. Being honest, I have a plan to remove this extra parameter. It might not be obvious looking at the current patch, but next patch will show that we can avoid introducing it at all.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
[On Arm only]
Tested-by: Wei Chen <Wei.Chen@xxxxxxx>

Please note, this is a split/cleanup/hardening of Julien's PoC:
"Add support for Guest IO forwarding to a device emulator"

Changes RFC -> V1:
    - was squashed with:
      "[RFC PATCH V1 09/12] libxl: Handle virtio-mmio irq in more correct way"       "[RFC PATCH V1 11/12] libxl: Insert "dma-coherent" property into virtio-mmio device node"
      "[RFC PATCH V1 12/12] libxl: Fix duplicate memory node in DT"
    - move VirtIO MMIO #define-s to xen/include/public/arch-arm.h

Changes V1 -> V2:
    - update the author of a patch

Changes V2 -> V3:
    - no changes

Changes V3 -> V4:
    - no changes
  tools/libs/light/libxl_arm.c     | 58 ++++++++++++++++++++++++++++++++++++++--
  tools/libs/light/libxl_types.idl |  1 +
  tools/xl/xl_parse.c              |  1 +
  xen/include/public/arch-arm.h    |  5 ++++
  4 files changed, 63 insertions(+), 2 deletions(-)

diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
index 66e8a06..588ee5a 100644
--- a/tools/libs/light/libxl_arm.c
+++ b/tools/libs/light/libxl_arm.c
@@ -26,8 +26,8 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
      uint32_t nr_spis = 0;
      unsigned int i;
-    uint32_t vuart_irq;
-    bool vuart_enabled = false;
+    uint32_t vuart_irq, virtio_irq;
+    bool vuart_enabled = false, virtio_enabled = false;
       * If pl011 vuart is enabled then increment the nr_spis to allow allocation
@@ -39,6 +39,17 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
          vuart_enabled = true;
  +    /*
+     * XXX: Handle properly virtio
+     * A proper solution would be the toolstack to allocate the interrupts +     * used by each virtio backend and let the backend now which one is used
+     */
+    if (libxl_defbool_val(d_config->b_info.arch_arm.virtio)) {
+        nr_spis += (GUEST_VIRTIO_MMIO_SPI - 32) + 1;
+        virtio_irq = GUEST_VIRTIO_MMIO_SPI;
+        virtio_enabled = true;
+    }
      for (i = 0; i < d_config->b_info.num_irqs; i++) {
          uint32_t irq = d_config->b_info.irqs[i];
          uint32_t spi;
@@ -58,6 +69,12 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
              return ERROR_FAIL;
  +        /* The same check as for vpl011 */
+        if (virtio_enabled && irq == virtio_irq) {
+            LOG(ERROR, "Physical IRQ %u conflicting with virtio SPI\n", irq);
+            return ERROR_FAIL;
+        }
          if (irq < 32)
  @@ -658,6 +675,39 @@ static int make_vpl011_uart_node(libxl__gc *gc, void *fdt,
      return 0;
  +static int make_virtio_mmio_node(libxl__gc *gc, void *fdt,
+                                 uint64_t base, uint32_t irq)
+    int res;
+    gic_interrupt intr;
+    /* Placeholder for virtio@ + a 64-bit number + \0 */
+    char buf[24];
+    snprintf(buf, sizeof(buf), "virtio@%"PRIx64, base);
+    res = fdt_begin_node(fdt, buf);
+    if (res) return res;
+    res = fdt_property_compat(gc, fdt, 1, "virtio,mmio");
+    if (res) return res;
+    res = fdt_property_regs(gc, fdt, GUEST_ROOT_ADDRESS_CELLS, GUEST_ROOT_SIZE_CELLS,
+                            1, base, GUEST_VIRTIO_MMIO_SIZE);
+    if (res) return res;
+    set_interrupt(intr, irq, 0xf, DT_IRQ_TYPE_EDGE_RISING);
+    res = fdt_property_interrupts(gc, fdt, &intr, 1);
+    if (res) return res;
+    res = fdt_property(fdt, "dma-coherent", NULL, 0);
+    if (res) return res;
+    res = fdt_end_node(fdt);
+    if (res) return res;
+    return 0;
  static const struct arch_info *get_arch_info(libxl__gc *gc,
                                               const struct xc_dom_image *dom)
@@ -961,6 +1011,9 @@ next_resize:
          if (info->tee == LIBXL_TEE_TYPE_OPTEE)
              FDT( make_optee_node(gc, fdt) );
  +        if (libxl_defbool_val(info->arch_arm.virtio))
+            FDT( make_virtio_mmio_node(gc, fdt, GUEST_VIRTIO_MMIO_BASE, GUEST_VIRTIO_MMIO_SPI) ); > +
          if (pfdt)
              FDT( copy_partial_fdt(gc, fdt, pfdt) );
  @@ -1178,6 +1231,7 @@ void libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
      /* ACPI is disabled by default */
      libxl_defbool_setdefault(&b_info->acpi, false);
+    libxl_defbool_setdefault(&b_info->arch_arm.virtio, false);
        if (b_info->type != LIBXL_DOMAIN_TYPE_PV)
diff --git a/tools/libs/light/libxl_types.idl b/tools/libs/light/libxl_types.idl
index 0532473..839df86 100644
--- a/tools/libs/light/libxl_types.idl
+++ b/tools/libs/light/libxl_types.idl
@@ -640,6 +640,7 @@ libxl_domain_build_info = Struct("domain_build_info",[
          ("arch_arm", Struct(None, [("gic_version", libxl_gic_version),
+                               ("virtio", libxl_defbool),

Regardless the question above, this doesn't sound very Arm specific.


I think we want to get the virtio configuration arch-agnostic because an admin should not need to know the arch internal to be able to assign virtio devices.

sounds reasonable

That said, you can leave it completely unimplemented for anything other than Arm.

got it

If you add new parameters in the idl, you will also want to introduce a define in libxl.h so an external toolstack (such as libvirt) can detect whether the field is supported by the installed version of libxl. See the other LIBXL_HAVE_*.

hmm, I didn't know about that, thank you.

                                 ("vuart", libxl_vuart_type),
      # Alternate p2m is not bound to any architecture or guest type, as it is
diff --git a/tools/xl/xl_parse.c b/tools/xl/xl_parse.c
index 4ebf396..2a3364b 100644
--- a/tools/xl/xl_parse.c
+++ b/tools/xl/xl_parse.c
@@ -2581,6 +2581,7 @@ skip_usbdev:
        xlu_cfg_get_defbool(config, "dm_restrict", &b_info->dm_restrict, 0);
+    xlu_cfg_get_defbool(config, "virtio", &b_info->arch_arm.virtio, 0);

Regardless the question above, any addition in the configuration file should be documented docs/man/xl.cfg.5.pod.in.

yes, documentation is my nearest plan.

        if (c_info->type == LIBXL_DOMAIN_TYPE_HVM) {
          if (!xlu_cfg_get_string (config, "vga", &buf, 0)) {
diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
index c365b1b..be7595f 100644
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -464,6 +464,11 @@ typedef uint64_t xen_callback_t;
  #define PSCI_cpu_on      2
  #define PSCI_migrate     3
  +/* VirtIO MMIO definitions */
+#define GUEST_VIRTIO_MMIO_BASE  xen_mk_ullong(0x02000000)

You will want to define any new region with the other *_{BASE, SIZE} above. Note that they should be ordered from bottom to the top of the memory layout.

I got it, this one should be put at the very beginning (before vGIC v2 mappings).

+#define GUEST_VIRTIO_MMIO_SIZE xen_mk_ullong(0x200)

AFAICT, the size of the virtio mmio region should be 0x100. So why is it 0x200?

I didn't find the total size requirement for the mmio region in virtio specification v1.1 (the size of control registers is indeed 0x100 and device-specific configuration registers starts at the offset 0x100, however it's size depends on the device and the driver).

kvmtool uses 0x200 [1], in some Linux device-trees we can see 0x200 [2] (however, device-tree bindings example has 0x100 [3]), so what would be the proper value for Xen code?


This will want to be defined with the other GUEST_*_SPI above.


Most likely, you will want to reserve a range

it seems yes, good point. BTW, the range is needed for the mmio region as well, correct?


[1] https://git.kernel.org/pub/scm/linux/kernel/git/will/kvmtool.git/tree/include/kvm/virtio-mmio.h#n9 [2] https://elixir.bootlin.com/linux/v5.11-rc3/source/arch/arm64/boot/dts/arm/foundation-v8.dtsi#L226 [3] https://elixir.bootlin.com/linux/v5.11-rc3/source/Documentation/devicetree/bindings/virtio/mmio.txt#L31


Oleksandr Tyshchenko



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