[PATCH v4 1/8] xen/arm: introduce static shared memory

[Penny Zheng <Penny.Zheng@arm.com>]

From: Penny Zheng <penny.zheng@arm.com>

This patch serie introduces a new feature: setting up static
shared memory on a dom0less system, through device tree configuration.

This commit parses shared memory node at boot-time, and reserve it in
bootinfo.reserved_mem to avoid other use.

This commits proposes a new Kconfig CONFIG_STATIC_SHM to wrap
static-shm-related codes, and this option depends on static memory(
CONFIG_STATIC_MEMORY). That's because that later we want to reuse a few
helpers, guarded with CONFIG_STATIC_MEMORY, like acquire_staticmem_pages, etc,
on static shared memory.

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
---
v4 change:
- nit fix on doc
---
v3 change:
- make nr_shm_domain unsigned int
---
v2 change:
- document refinement
- remove bitmap and use the iteration to check
- add a new field nr_shm_domain to keep the number of shared domain
---
 docs/misc/arm/device-tree/booting.txt | 120 ++++++++++++++++++++++++++
 xen/arch/arm/Kconfig                  |   6 ++
 xen/arch/arm/bootfdt.c                |  68 +++++++++++++++
 xen/arch/arm/include/asm/setup.h      |   3 +
 4 files changed, 197 insertions(+)

diff --git a/docs/misc/arm/device-tree/booting.txt b/docs/misc/arm/device-tree/booting.txt
index 7b4a29a2c2..b2a7f3f590 100644
--- a/docs/misc/arm/device-tree/booting.txt
+++ b/docs/misc/arm/device-tree/booting.txt
@@ -360,3 +360,123 @@ device-tree:
 
 This will reserve a 512MB region starting at the host physical address
 0x30000000 to be exclusively used by DomU1.
+
+Static Shared Memory
+====================
+
+The static shared memory device tree nodes allow users to statically set up
+shared memory on dom0less system, enabling domains to do shm-based
+communication.
+
+- compatible
+
+    "xen,domain-shared-memory-v1"
+
+- xen,shm-id
+
+    An 8-bit integer that represents the unique identifier of the shared memory
+    region. The maximum identifier shall be "xen,shm-id = <0xff>".
+
+- xen,shared-mem
+
+    An array takes a physical address, which is the base address of the
+    shared memory region in host physical address space, a size, and a guest
+    physical address, as the target address of the mapping. The number of cells
+    for the host address (and size) is the same as the guest pseudo-physical
+    address and they are inherited from the parent node.
+
+- role (Optional)
+
+    A string property specifying the ownership of a shared memory region,
+    the value must be one of the following: "owner", or "borrower"
+    A shared memory region could be explicitly backed by one domain, which is
+    called "owner domain", and all the other domains who are also sharing
+    this region are called "borrower domain".
+    If not specified, the default value is "borrower" and owner is
+    "dom_shared", a system domain.
+
+As an example:
+
+chosen {
+    #address-cells = <0x1>;
+    #size-cells = <0x1>;
+    xen,xen-bootargs = "console=dtuart dtuart=serial0 bootscrub=0";
+
+    ......
+
+    /* this is for Dom0 */
+    dom0-shared-mem@10000000 {
+        compatible = "xen,domain-shared-memory-v1";
+        role = "owner";
+        xen,shm-id = <0x0>;
+        xen,shared-mem = <0x10000000 0x10000000 0x10000000>;
+    }
+
+    domU1 {
+        compatible = "xen,domain";
+        #address-cells = <0x1>;
+        #size-cells = <0x1>;
+        memory = <0 131072>;
+        cpus = <2>;
+        vpl011;
+
+        /*
+         * shared memory region identified as 0x0(xen,shm-id = <0x0>)
+         * is shared between Dom0 and DomU1.
+         */
+        domU1-shared-mem@10000000 {
+            compatible = "xen,domain-shared-memory-v1";
+            role = "borrower";
+            xen,shm-id = <0x0>;
+            xen,shared-mem = <0x10000000 0x10000000 0x50000000>;
+        }
+
+        /*
+         * shared memory region identified as 0x1(xen,shm-id = <0x1>)
+         * is shared between DomU1 and DomU2.
+         */
+        domU1-shared-mem@50000000 {
+            compatible = "xen,domain-shared-memory-v1";
+            xen,shm-id = <0x1>;
+            xen,shared-mem = <0x50000000 0x20000000 0x60000000>;
+        }
+
+        ......
+
+    };
+
+    domU2 {
+        compatible = "xen,domain";
+        #address-cells = <0x1>;
+        #size-cells = <0x1>;
+        memory = <0 65536>;
+        cpus = <1>;
+
+        /*
+         * shared memory region identified as 0x1(xen,shm-id = <0x1>)
+         * is shared between domU1 and domU2.
+         */
+        domU2-shared-mem@50000000 {
+            compatible = "xen,domain-shared-memory-v1";
+            xen,shm-id = <0x1>;
+            xen,shared-mem = <0x50000000 0x20000000 0x70000000>;
+        }
+
+        ......
+    };
+};
+
+This is an example with two static shared memory regions.
+
+For the static shared memory region identified as 0x0, host physical
+address starting at 0x10000000 of 256MB will be reserved to be shared between
+Dom0 and DomU1. It will get mapped at 0x10000000 in Dom0 guest physical address
+space, and at 0x50000000 in DomU1 guest physical address space. Dom0 is
+explicitly defined as the owner domain, and DomU1 is the borrower domain.
+
+For the static shared memory region identified as 0x1, host physical
+address starting at 0x50000000 of 512MB will be reserved to be shared between
+DomU1 and DomU2. It will get mapped at 0x60000000 in DomU1 guest physical
+address space, and at 0x70000000 in DomU2 guest physical address space. DomU1
+and DomU2 are both the borrower domain, the owner domain is the default owner
+domain dom_shared.
diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
index ecfa6822e4..5ee9921f56 100644
--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -106,6 +106,12 @@ config TEE
 
 source "arch/arm/tee/Kconfig"
 
+config STATIC_SHM
+	bool "Statically shared memory on a dom0less system" if UNSUPPORTED
+	depends on STATIC_MEMORY
+	help
+	  This option enables statically shared memory on a dom0less system.
+
 endmenu
 
 menu "ARM errata workaround via the alternative framework"
diff --git a/xen/arch/arm/bootfdt.c b/xen/arch/arm/bootfdt.c
index 29671c8df0..c8e8747c3e 100644
--- a/xen/arch/arm/bootfdt.c
+++ b/xen/arch/arm/bootfdt.c
@@ -360,6 +360,70 @@ static int __init process_domain_node(const void *fdt, int node,
                                    size_cells, &bootinfo.reserved_mem, true);
 }
 
+#ifdef CONFIG_STATIC_SHM
+static int __init process_shm_node(const void *fdt, int node,
+                                   u32 address_cells, u32 size_cells)
+{
+    const struct fdt_property *prop;
+    const __be32 *cell;
+    paddr_t paddr, size;
+    struct meminfo *mem = &bootinfo.reserved_mem;
+    unsigned long i;
+
+    if ( address_cells < 1 || size_cells < 1 )
+    {
+        printk("fdt: invalid #address-cells or #size-cells for static shared memory node.\n");
+        return -EINVAL;
+    }
+
+    prop = fdt_get_property(fdt, node, "xen,shared-mem", NULL);
+    if ( !prop )
+        return -ENOENT;
+
+    /*
+     * xen,shared-mem = <paddr, size, gaddr>;
+     * Memory region starting from physical address #paddr of #size shall
+     * be mapped to guest physical address #gaddr as static shared memory
+     * region.
+     */
+    cell = (const __be32 *)prop->data;
+    device_tree_get_reg(&cell, address_cells, size_cells, &paddr, &size);
+    for ( i = 0; i < mem->nr_banks; i++ )
+    {
+        /*
+         * A static shared memory region could be shared between multiple
+         * domains.
+         */
+        if ( paddr == mem->bank[i].start && size == mem->bank[i].size )
+            break;
+    }
+
+    if ( i == mem->nr_banks )
+    {
+        if ( i < NR_MEM_BANKS )
+        {
+            /* Static shared memory shall be reserved from any other use. */
+            mem->bank[mem->nr_banks].start = paddr;
+            mem->bank[mem->nr_banks].size = size;
+            mem->bank[mem->nr_banks].xen_domain = true;
+            mem->nr_banks++;
+        }
+        else
+        {
+            printk("Warning: Max number of supported memory regions reached.\n");
+            return -ENOSPC;
+        }
+    }
+    /*
+     * keep a count of the number of domains, which later may be used to
+     * calculate the number of the reference count.
+     */
+    mem->bank[i].nr_shm_domain++;
+
+    return 0;
+}
+#endif
+
 static int __init early_scan_node(const void *fdt,
                                   int node, const char *name, int depth,
                                   u32 address_cells, u32 size_cells,
@@ -380,6 +444,10 @@ static int __init early_scan_node(const void *fdt,
         process_chosen_node(fdt, node, name, address_cells, size_cells);
     else if ( depth == 2 && device_tree_node_compatible(fdt, node, "xen,domain") )
         rc = process_domain_node(fdt, node, name, address_cells, size_cells);
+#ifdef CONFIG_STATIC_SHM
+    else if ( depth <= 3 && device_tree_node_compatible(fdt, node, "xen,domain-shared-memory-v1") )
+        rc = process_shm_node(fdt, node, address_cells, size_cells);
+#endif
 
     if ( rc < 0 )
         printk("fdt: node `%s': parsing failed\n", name);
diff --git a/xen/arch/arm/include/asm/setup.h b/xen/arch/arm/include/asm/setup.h
index 7a1e1d6798..35449bd7d8 100644
--- a/xen/arch/arm/include/asm/setup.h
+++ b/xen/arch/arm/include/asm/setup.h
@@ -27,6 +27,9 @@ struct membank {
     paddr_t start;
     paddr_t size;
     bool xen_domain; /* whether the memory bank is bound to a Xen domain. */
+#ifdef CONFIG_STATIC_SHM
+    unsigned int nr_shm_domain;
+#endif
 };
 
 struct meminfo {
-- 
2.25.1