[PATCH v2 6/6] xen/arm: Add capabilities to dom0less

[Jason Andryuk <jason.andryuk@xxxxxxx>]

Add capabilities property to dom0less to allow building a
disaggregated system.  Only a single hardware domain and single xenstore
domain can be specified.  Multiple control domains are possible.

Introduce bootfdt.h to contain these constants.

When using the hardware or xenstore capabilities, adjust the grant and
event channel limits similar to dom0.

For a hardware domain, require an IOMMU and disallow specifying a vpl011
console or nr_spis.

Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
---
v2:
Fix comment style
Make DOMAIN_CAPS_* unsigned
Remove forced directmap & iommu
Require iommu with use of hardware domain
Limit to a single xenstore domain

There is overlap with hyperlaunch.  The numeric values are the same.
Hyperlaunch doesn't expose the values in a public header as done here.
Is this to be expected for dom0less?  It seems most of dom0less isn't in
a header, but just in docs.

Hyperlaunch uses BUILD_CAPS_, but I chose DOMAIN_CAPS_ since there are
domain-level capabilities.

Only a single xenstore and hardware domain make sense.  Hardware domain
receiving all hardware can only have a single domain.

For Xenstore, the logic latches the single xs_domid and uses that for
all domains.  Also, only a single domain can register for VIRQ_DOM_EXC.
---
 docs/misc/arm/device-tree/booting.txt | 11 ++++++++
 xen/arch/arm/dom0less-build.c         | 39 +++++++++++++++++++++++++++
 xen/arch/arm/domain.c                 |  3 ++-
 xen/include/public/bootfdt.h          | 31 +++++++++++++++++++++
 4 files changed, 83 insertions(+), 1 deletion(-)
 create mode 100644 xen/include/public/bootfdt.h

diff --git a/docs/misc/arm/device-tree/booting.txt 
b/docs/misc/arm/device-tree/booting.txt
index ac781c9cc8..490c792ddf 100644
--- a/docs/misc/arm/device-tree/booting.txt
+++ b/docs/misc/arm/device-tree/booting.txt
@@ -167,6 +167,17 @@ with the following properties:
     Refer to docs/misc/cache_coloring.rst for syntax. This option is applicable
     only to Arm64 guests.
 
+- capabilities
+    Optional.  A bit field of domain capabilities for a disaggregated
+    system.  A traditional dom0 has all all of these capabilities, and a
+    domU has none of them.
+
+    0x1 DOMAIN_CAPS_CONTROL  - A privileged, control domain
+    0x2 DOMAIN_CAPS_HARDWARE - The hardware domain - there can be only 1
+    0x4 DOMAIN_CAPS_XENSTORE - The xenstore domain - there can be only 1
+
+    The default is no capabilities.
+
 - vpl011
 
     An empty property to enable/disable a virtual pl011 for the guest to
diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
index fc515c9852..1cb6c170a7 100644
--- a/xen/arch/arm/dom0less-build.c
+++ b/xen/arch/arm/dom0less-build.c
@@ -12,6 +12,7 @@
 #include <xen/sizes.h>
 #include <xen/vmap.h>
 
+#include <public/bootfdt.h>
 #include <public/io/xs_wire.h>
 
 #include <asm/arm64/sve.h>
@@ -906,6 +907,8 @@ static int __init construct_domU(struct domain *d,
            d->max_vcpus, mem);
 
     kinfo.vpl011 = dt_property_read_bool(node, "vpl011");
+    if ( kinfo.vpl011 && is_hardware_domain(d) )
+        panic("hardware domain cannot specify vpl011\n");
 
     rc = dt_property_read_string(node, "xen,enhanced", &dom0less_enhanced);
     if ( rc == -EILSEQ ||
@@ -1020,6 +1023,40 @@ void __init create_domUs(void)
         if ( (max_init_domid + 1) >= DOMID_FIRST_RESERVED )
             panic("No more domain IDs available\n");
 
+        if ( dt_property_read_u32(node, "capabilities", &val) )
+        {
+            if ( val & ~DOMAIN_CAPS_MASK )
+                panic("Invalid capabilities (%"PRIx32")\n", val);
+
+            if ( val & DOMAIN_CAPS_CONTROL )
+                flags |= CDF_privileged;
+
+            if ( val & DOMAIN_CAPS_HARDWARE )
+            {
+                if ( hardware_domain )
+                    panic("Only 1 hardware domain can be specified! (%pd)\n",
+                           hardware_domain);
+
+                if ( !iommu_enabled )
+                    panic("iommu required for dom0less hardware domain\n");
+
+                d_cfg.max_grant_frames = gnttab_dom0_frames();
+                d_cfg.max_evtchn_port = -1;
+                flags |= CDF_hardware;
+                iommu = true;
+            }
+
+            if ( val & DOMAIN_CAPS_XENSTORE )
+            {
+                if ( xs_domid != DOMID_INVALID )
+                    panic("Only 1 xenstore domain can be specified! (%u)\n",
+                          xs_domid);
+
+                d_cfg.flags |= XEN_DOMCTL_CDF_xs_domain;
+                d_cfg.max_evtchn_port = -1;
+            }
+        }
+
         if ( dt_find_property(node, "xen,static-mem", NULL) )
         {
             if ( llc_coloring_enabled )
@@ -1082,6 +1119,8 @@ void __init create_domUs(void)
                 d_cfg.arch.nr_spis = MAX(d_cfg.arch.nr_spis,
                                          vpl011_virq - 32 + 1);
         }
+        else if ( flags & CDF_hardware )
+            panic("nr_spis cannot be specified for hardware domain\n");
 
         /* Get the optional property domain-cpupool */
         cpupool_node = dt_parse_phandle(node, "domain-cpupool", 0);
diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 3ba959f866..dc4b4e84c1 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -608,7 +608,8 @@ int arch_sanitise_domain_config(struct 
xen_domctl_createdomain *config)
 {
     unsigned int max_vcpus;
     unsigned int flags_required = (XEN_DOMCTL_CDF_hvm | XEN_DOMCTL_CDF_hap);
-    unsigned int flags_optional = (XEN_DOMCTL_CDF_iommu | XEN_DOMCTL_CDF_vpmu);
+    unsigned int flags_optional = (XEN_DOMCTL_CDF_iommu | XEN_DOMCTL_CDF_vpmu |
+                                   XEN_DOMCTL_CDF_xs_domain );
     unsigned int sve_vl_bits = sve_decode_vl(config->arch.sve_vl);
 
     if ( (config->flags & ~flags_optional) != flags_required )
diff --git a/xen/include/public/bootfdt.h b/xen/include/public/bootfdt.h
new file mode 100644
index 0000000000..86c46b42a9
--- /dev/null
+++ b/xen/include/public/bootfdt.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Xen Device Tree boot information
+ *
+ * Information for configuring Xen domains created at boot time.
+ */
+
+#ifndef __XEN_PUBLIC_BOOTFDT_H__
+#define __XEN_PUBLIC_BOOTFDT_H__
+
+/*
+ * Domain Capabilities specified in the "capabilities" property.  Use of
+ * this property allows splitting up the monolithic dom0 into separate,
+ * less privileged components.  A regular domU has no capabilities
+ * (which is the default if nothing is specified).  A traditional dom0
+ * has all three capabilities.
+ */
+
+/* Control/Privileged domain capable of affecting other domains. */
+#define DOMAIN_CAPS_CONTROL  (1U << 0)
+/*
+ * Hardware domain controlling physical hardware.  Typically providing
+ * backends to other domains.
+ */
+#define DOMAIN_CAPS_HARDWARE (1U << 1)
+/* Xenstore domain. */
+#define DOMAIN_CAPS_XENSTORE (1U << 2)
+#define DOMAIN_CAPS_MASK     (DOMAIN_CAPS_CONTROL | DOMAIN_CAPS_HARDWARE | \
+                              DOMAIN_CAPS_XENSTORE)
+
+#endif /* __XEN_PUBLIC_BOOTFDT_H__ */
-- 
2.49.0