xen/arm: introduce xen-evtchn dom0less property

Introduce a new sub-node under /chosen node to establish static event
channel communication between domains on dom0less systems.

An event channel will be created beforehand to allow the domains to
send notifications to each other.

Signed-off-by: Rahul Singh <rahul.singh@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

docs/misc/arm/device-tree/booting.txt

@@ -382,3 +382,101 @@ device-tree:
 
 This will reserve a 512MB region starting at the host physical address
 0x30000000 to be exclusively used by DomU1.
+
+Static Event Channel
+====================
+The event channel communication will be established statically between two
+domains (dom0 and domU also). Event channel connection information between
+domains will be passed to Xen via the device tree node. The event channel
+will be created and established in Xen before the domain started. The domain
+does not need to do any operation to establish a connection. Domain only
+needs hypercall EVTCHNOP_send(local port) to send notifications to the
+remote guest.
+
+There is no need to describe the static event channel info in the domU device
+tree. Static event channels are only useful in fully static configurations,
+and in those configurations, the domU device tree dynamically generated by Xen
+is not needed.
+
+To enable the event-channel interface for domU guests include the
+xen,enhanced = "no-xenstore" property in the domU Xen device tree node.
+
+Under the "xen,domain" compatible node for domU, there needs to be sub-nodes
+with compatible "xen,evtchn" that describe the event channel connection
+between two domUs. For dom0, there needs to be sub-nodes with compatible
+"xen,evtchn" under the chosen node.
+
+The static event channel node has the following properties:
+
+- compatible
+
+    "xen,evtchn"
+
+- xen,evtchn
+
+    The property is tuples of two numbers
+    (local-evtchn link-to-foreign-evtchn) where:
+
+    local-evtchn is an integer value that will be used to allocate local port
+    for a domain to send and receive event notifications to/from the remote
+    domain. Maximum supported value is 2^17 for FIFO ABI and 4096 for 2L ABI.
+    It is recommended to use low event channel IDs.
+
+    link-to-foreign-evtchn is a single phandle to a remote evtchn to which
+    local-evtchn will be connected.
+
+Example
+=======
+
+chosen {
+
+    /* One sub-node per local event channel. This sub-node is for Dom0. */
+    ec1: evtchn@1 {
+         compatible = "xen,evtchn-v1";
+         /* local-evtchn link-to-foreign-evtchn */
+         xen,evtchn = <0xa &ec2>;
+    };
+
+    domU1 {
+        compatible = "xen,domain";
+        #address-cells = <0x2>;
+        #size-cells = <0x1>;
+        xen,enhanced = "no-xenstore";
+
+        /* One sub-node per local event channel */
+        ec2: evtchn@2 {
+            compatible = "xen,evtchn-v1";
+            /* local-evtchn link-to-foreign-evtchn */
+            xen,evtchn = <0xa &ec1>;
+        };
+
+        ec3: evtchn@3 {
+            compatible = "xen,evtchn-v1";
+            xen,evtchn = <0xb &ec5>;
+        };
+
+        ec4: evtchn@4 {
+            compatible = "xen,evtchn-v1";
+            xen,evtchn = <0xc &ec6>;
+        };
+    };
+
+    domU2 {
+        compatible = "xen,domain";
+        #address-cells = <0x2>;
+        #size-cells = <0x1>;
+        xen,enhanced = "no-xenstore";
+
+        /* One sub-node per local event channel */
+        ec5: evtchn@5 {
+            compatible = "xen,evtchn-v1";
+            /* local-evtchn link-to-foreign-evtchn */
+            xen,evtchn = <0xb &ec3>;
+        };
+
+        ec6: evtchn@6 {
+            compatible = "xen,evtchn-v1";
+            xen,evtchn = <0xd &ec4>;
+        };
+    };
+};

xen/arch/arm/domain_build.c

@@ -33,6 +33,8 @@
 #include <xen/grant_table.h>
 #include <xen/serial.h>
 
+#define STATIC_EVTCHN_NODE_SIZE_CELLS 2
+
 static unsigned int __initdata opt_dom0_max_vcpus;
 integer_param("dom0_max_vcpus", opt_dom0_max_vcpus);
 
@@ -3052,6 +3054,150 @@ void __init evtchn_allocate(struct domain *d)
     d->arch.hvm.params[HVM_PARAM_CALLBACK_IRQ] = val;
 }
 
+static int __init get_evtchn_dt_property(const struct dt_device_node *np,
+                                         uint32_t *port, uint32_t *phandle)
+{
+    const __be32 *prop = NULL;
+    uint32_t len;
+
+    prop = dt_get_property(np, "xen,evtchn", &len);
+    if ( !prop )
+    {
+        printk(XENLOG_ERR "xen,evtchn property should not be empty.\n");
+        return -EINVAL;
+    }
+
+    if ( !len || len < dt_cells_to_size(STATIC_EVTCHN_NODE_SIZE_CELLS) )
+    {
+        printk(XENLOG_ERR "xen,evtchn property value is not valid.\n");
+        return -EINVAL;
+    }
+
+    *port = dt_next_cell(1, &prop);
+    *phandle = dt_next_cell(1, &prop);
+
+    return 0;
+}
+
+static int __init alloc_domain_evtchn(struct dt_device_node *node)
+{
+    int rc;
+    uint32_t domU1_port, domU2_port, remote_phandle;
+    struct dt_device_node *remote_node;
+    const struct dt_device_node *p1_node, *p2_node;
+    struct evtchn_alloc_unbound alloc_unbound;
+    struct evtchn_bind_interdomain bind_interdomain;
+    struct domain *d1 = NULL, *d2 = NULL;
+
+    if ( !dt_device_is_compatible(node, "xen,evtchn-v1") )
+        return 0;
+
+    /*
+     * Event channel is already created while parsing the other side of
+     * evtchn node.
+     */
+    if ( dt_device_static_evtchn_created(node) )
+        return 0;
+
+    rc = get_evtchn_dt_property(node, &domU1_port, &remote_phandle);
+    if ( rc )
+        return rc;
+
+    remote_node = dt_find_node_by_phandle(remote_phandle);
+    if ( !remote_node )
+    {
+        printk(XENLOG_ERR
+                "evtchn: could not find remote evtchn phandle\n");
+        return -EINVAL;
+    }
+
+    rc = get_evtchn_dt_property(remote_node, &domU2_port, &remote_phandle);
+    if ( rc )
+        return rc;
+
+    if ( node->phandle != remote_phandle )
+    {
+        printk(XENLOG_ERR "xen,evtchn property is not setup correctly.\n");
+        return -EINVAL;
+    }
+
+    p1_node = dt_get_parent(node);
+    if ( !p1_node )
+    {
+        printk(XENLOG_ERR "evtchn: evtchn parent node is NULL\n" );
+        return -EINVAL;
+    }
+
+    p2_node = dt_get_parent(remote_node);
+    if ( !p2_node )
+    {
+        printk(XENLOG_ERR "evtchn: remote parent node is NULL\n" );
+        return -EINVAL;
+    }
+
+    d1 = get_domain_by_id(p1_node->used_by);
+    d2 = get_domain_by_id(p2_node->used_by);
+
+    if ( !d1 || !d2 )
+    {
+        printk(XENLOG_ERR "evtchn: could not find domains\n" );
+        return -EINVAL;
+    }
+
+    alloc_unbound.dom = d1->domain_id;
+    alloc_unbound.remote_dom = d2->domain_id;
+
+    rc = evtchn_alloc_unbound(&alloc_unbound, domU1_port);
+    if ( rc < 0 )
+    {
+        printk(XENLOG_ERR
+                "evtchn_alloc_unbound() failure (Error %d) \n", rc);
+        return rc;
+    }
+
+    bind_interdomain.remote_dom  = d1->domain_id;
+    bind_interdomain.remote_port = domU1_port;
+
+    rc = evtchn_bind_interdomain(&bind_interdomain, d2, domU2_port);
+    if ( rc < 0 )
+    {
+        printk(XENLOG_ERR
+                "evtchn_bind_interdomain() failure (Error %d) \n", rc);
+        return rc;
+    }
+
+    dt_device_set_static_evtchn_created(node);
+    dt_device_set_static_evtchn_created(remote_node);
+
+    return 0;
+}
+
+void __init alloc_static_evtchn(void)
+{
+    struct dt_device_node *node, *evtchn_node;
+    struct dt_device_node *chosen = dt_find_node_by_path("/chosen");
+
+    BUG_ON(chosen == NULL);
+
+    if ( hardware_domain )
+        dt_device_set_used_by(chosen, hardware_domain->domain_id);
+
+    dt_for_each_child_node(chosen, node)
+    {
+        if ( hardware_domain )
+        {
+            if ( alloc_domain_evtchn(node) != 0 )
+                panic("Could not set up domains evtchn\n");
+        }
+
+        dt_for_each_child_node(node, evtchn_node)
+        {
+            if ( alloc_domain_evtchn(evtchn_node) != 0 )
+                panic("Could not set up domains evtchn\n");
+        }
+    }
+}
+
 static void __init find_gnttab_region(struct domain *d,
                                       struct kernel_info *kinfo)
 {
@@ -3369,6 +3515,7 @@ void __init create_domUs(void)
             panic("Error creating domain %s\n", dt_node_name(node));
 
         d->is_console = true;
+        dt_device_set_used_by(node, d->domain_id);
 
         if ( construct_domU(d, node) != 0 )
             panic("Could not set up domain %s\n", dt_node_name(node));

xen/arch/arm/include/asm/setup.h

@@ -106,6 +106,7 @@ int acpi_make_efi_nodes(void *fdt, struct membank tbl_add[]);
 
 void create_domUs(void);
 void create_dom0(void);
+void alloc_static_evtchn(void);
 
 void discard_initial_modules(void);
 void fw_unreserved_regions(paddr_t s, paddr_t e,

xen/arch/arm/setup.c

@@ -1078,6 +1078,8 @@ void __init start_xen(unsigned long boot_phys_offset,
     if ( acpi_disabled )
         create_domUs();
 
+    alloc_static_evtchn();
+
     /*
      * This needs to be called **before** heap_init_late() so modules
      * will be scrubbed (unless suppressed).

xen/include/xen/device_tree.h

@@ -92,6 +92,10 @@ struct dt_device_node {
 
     /* IOMMU specific fields */
     bool is_protected;
+
+    /* HACK: Remove this if there is a need of space */
+    bool_t static_evtchn_created;
+
     /*
      * The main purpose of this list is to link the structure in the list
      * of devices assigned to domain.
@@ -317,6 +321,18 @@ static inline bool_t dt_property_name_is_equal(const struct dt_property *pp,
     return !dt_prop_cmp(pp->name, name);
 }
 
+static inline void
+dt_device_set_static_evtchn_created(struct dt_device_node *device)
+{
+    device->static_evtchn_created = true;
+}
+
+static inline bool_t
+dt_device_static_evtchn_created(const struct dt_device_node *device)
+{
+    return device->static_evtchn_created;
+}
+
 /**
  * dt_find_compatible_node - Find a node based on type and one of the
  *                           tokens in its "compatible" property