[xen staging] xen/riscv: add initial dom0less infrastructure support

[patchbot@xxxxxxx]

commit 1043866f84f36fa0016d8c0dff20d8daa478bb75
Author:     Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
AuthorDate: Wed Sep 23 12:26:49 2026 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Sep 30 15:00:25 2026 +0200

    xen/riscv: add initial dom0less infrastructure support
    
    Enable dom0less support for RISC-V by selecting HAS_DOM0LESS and
    providing the minimal architecture hooks required by the common
    dom0less infrastructure.
    
    Add stub implementations for architecture-specific helpers used when
    building domains from the device tree. These allow the generic
    dom0less code to build and let a basic DomU be constructed on RISC-V.
    construct_hwdom() and make_hypervisor_node() are still stubs returning
    an error: Dom0/hwdom construction isn't supported yet, and the
    hypervisor node generation (needed by domains with
    DOM0LESS_ENHANCED_NO_XS set) is not implemented. Both are marked with
    a TODO and are not reached by the currently supported configurations.
    
    Provide missing helpers and definitions required by the domain
    construction code, including domain bitness helpers and the
    p2m_set_allocation() prototype.
    
    Additionally define the guest magic memory region (GUEST_MAGIC_BASE /
    GUEST_MAGIC_SIZE) in asm/guest-layout.h. The base is arbitrary; the
    only constraint is that the region must not overlap guest RAM or the
    emulated device regions. It is placed in the unused gap below
    GUEST_RAM0_BASE (0x80000000); the constraints are documented next to
    the #define-s.
    
    A separate region for grant tables will be introduced at the same time as
    the introduction of the grant table for RISC-V.
    
    Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/riscv/Kconfig                    |  2 ++
 xen/arch/riscv/dom0less-build.c           |  7 +++++++
 xen/arch/riscv/domain-build.c             | 28 ++++++++++++++++++++++++++++
 xen/arch/riscv/include/asm/guest-layout.h | 12 ++++++++++++
 4 files changed, 49 insertions(+)

diff --git a/xen/arch/riscv/Kconfig b/xen/arch/riscv/Kconfig
index 48520588fe..d8a348c0cf 100644
--- a/xen/arch/riscv/Kconfig
+++ b/xen/arch/riscv/Kconfig
@@ -6,6 +6,8 @@ config RISCV
        select GENERIC_BUG_FRAME
        select GENERIC_UART_INIT
        select HAS_DEVICE_TREE_DISCOVERY
+       select HAS_DOM0LESS
+       select HAS_DOMAIN_TYPE
        select HAS_EX_TABLE
        select HAS_PMAP
        select HAS_UBSAN
diff --git a/xen/arch/riscv/dom0less-build.c b/xen/arch/riscv/dom0less-build.c
index d1a51b9293..0801d7e250 100644
--- a/xen/arch/riscv/dom0less-build.c
+++ b/xen/arch/riscv/dom0less-build.c
@@ -102,3 +102,10 @@ int __init arch_parse_dom0less_node(struct dt_device_node 
*node,
 
     return 0;
 }
+
+int __init arch_handle_passthrough_prop(struct kernel_info *kinfo,
+                                        struct dt_device_node *node)
+{
+    /* Nothing specific to do for now */
+    return 0;
+}
diff --git a/xen/arch/riscv/domain-build.c b/xen/arch/riscv/domain-build.c
index d7613721db..1e3abe259c 100644
--- a/xen/arch/riscv/domain-build.c
+++ b/xen/arch/riscv/domain-build.c
@@ -156,9 +156,37 @@ int __init make_cpus_node(const struct domain *d, struct 
kernel_info *kinfo)
     return fdt_end_node(fdt);
 }
 
+int __init construct_hwdom(struct kernel_info *kinfo,
+                           const struct dt_device_node *node)
+{
+    /*
+     * TODO: Dom0/hwdom construction isn't supported on RISC-V yet, so this
+     * is a stub returning an error. It must be implemented before a hardware
+     * domain can be built from the device tree.
+     */
+
+    return -EOPNOTSUPP;
+}
+
 int __init make_timer_node(const struct kernel_info *kinfo)
 {
     /* There is no need for timer node for RISC-V. */
 
     return 0;
 }
+
+int __init make_hypervisor_node(struct domain *d,
+                                const struct kernel_info *kinfo,
+                                int addrcells, int sizecells)
+{
+    /*
+     * TODO: Generating the hypervisor node isn't implemented yet. Returning
+     * an error here breaks building of any domain (DomU included) whose
+     * dom0less_feature has DOM0LESS_ENHANCED_NO_XS set. This is harmless for
+     * now because Dom0/hwdom construction isn't supported on RISC-V yet
+     * either, and no RISC-V DomU sets that flag, so this path is never taken.
+     * It must be implemented before DOM0LESS_ENHANCED_NO_XS is used.
+     */
+
+    return -EOPNOTSUPP;
+}
diff --git a/xen/arch/riscv/include/asm/guest-layout.h 
b/xen/arch/riscv/include/asm/guest-layout.h
index 90603f06bb..ceed9125e7 100644
--- a/xen/arch/riscv/include/asm/guest-layout.h
+++ b/xen/arch/riscv/include/asm/guest-layout.h
@@ -32,4 +32,16 @@
 #define GUEST_RAM_BANK_BASES   { GUEST_RAM0_BASE, GUEST_RAM1_BASE }
 #define GUEST_RAM_BANK_SIZES   { GUEST_RAM0_SIZE, GUEST_RAM1_SIZE }
 
+/*
+ * The guest magic region holds the Xen-reserved pages mapped into the
+ * guest's physical address space. The only real constraint on
+ * GUEST_MAGIC_BASE/SIZE is that the region must not overlap guest RAM
+ * (the GUEST_RAMx banks) or the emulated device regions defined above;
+ * the exact base is otherwise arbitrary. Here it is placed in the unused gap
+ * below GUEST_RAM0_BASE (0x80000000), but a hole after a RAM bank would work
+ * equally well.
+ */
+#define GUEST_MAGIC_BASE  _UL(0x79000000)
+#define GUEST_MAGIC_SIZE  _UL(0x00200000)
+
 #endif /* ASM_RISCV_GUEST_LAYOUT_H */
--
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