xen: introduce domain-layout.h with common domain_use_host_layout()

domain_use_host_layout() is not architecture-specific and may be needed
on x86 [1]. Replace the ARM-specific macro in asm/domain.h with a common
static inline in a new dedicated header, xen/domain-layout.h.

xen/domain.h would be the natural home, but placing it there would
require including xen/paging.h (for paging_mode_translate()) and
xen/sched.h (for is_hardware_domain()), which would introduce circular
dependencies. A separate header that callers opt into avoids this.

Adjust the implementation to take paging_mode_translate() into account
so it works correctly for all architectures, including x86. Some extra
details about implementation [2] and [3].

To avoid the following compilation issue:

In file included from ./include/xen/paging.h:4,
                 from ./include/xen/domain-layout.h:6,
                 from common/device-tree/domain-build.c:4:
./arch/riscv/include/asm/paging.h:17:48: error: 'struct page_info'
declared inside parameter list will not be visible outside of this
definition or declaration [-Werror]
   17 | void paging_free_page(struct domain *d, struct page_info *pg);

add the forward declaration of struct page_info to RISC-V's asm/paging.h.

[1] https://lore.kernel.org/xen-devel/alpine.DEB.2.22.394.2602161038120.359097@ubuntu-linux-20-04-desktop/
[2] https://lore.kernel.org/xen-devel/alpine.DEB.2.22.394.2602271742400.3148344@ubuntu-linux-20-04-desktop/
[3] https://lore.kernel.org/xen-devel/alpine.DEB.2.22.394.2602271750190.3148344@ubuntu-linux-20-04-desktop/

Suggested-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Michal Orzel <michal.orzel@amd.com>

xen/arch/arm/domain_build.c

@@ -2,6 +2,7 @@
 #include <xen/init.h>
 #include <xen/bootinfo.h>
 #include <xen/compile.h>
+#include <xen/domain-layout.h>
 #include <xen/dom0less-build.h>
 #include <xen/fdt-domain-build.h>
 #include <xen/fdt-kernel.h>

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

@@ -18,20 +18,6 @@ struct hvm_domain
     uint64_t              params[HVM_NR_PARAMS];
 };
 
-/*
- * Is the domain using the host memory layout?
- *
- * Direct-mapped domain will always have the RAM mapped with GFN == MFN.
- * To avoid any trouble finding space, it is easier to force using the
- * host memory layout.
- *
- * The hardware domain will use the host layout regardless of
- * direct-mapped because some OS may rely on a specific address ranges
- * for the devices.
- */
-#define domain_use_host_layout(d) (is_domain_direct_mapped(d) || \
-                                   is_hardware_domain(d))
-
 struct vtimer {
     struct vcpu *v;
     int irq;

xen/arch/arm/vgic-v3.c

@@ -10,6 +10,7 @@
  */
 
 #include <xen/bitops.h>
+#include <xen/domain-layout.h>
 #include <xen/init.h>
 #include <xen/irq.h>
 #include <xen/lib.h>

xen/arch/riscv/include/asm/paging.h

@@ -4,6 +4,7 @@
 #include <asm-generic/paging.h>
 
 struct domain;
+struct page_info;
 
 int paging_domain_init(struct domain *d);
 

xen/common/device-tree/domain-build.c

@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
 #include <xen/bootinfo.h>
+#include <xen/domain-layout.h>
 #include <xen/fdt-domain-build.h>
 #include <xen/init.h>
 #include <xen/lib.h>

xen/include/xen/domain-layout.h

@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef XEN_DOMAIN_LAYOUT_H
+#define XEN_DOMAIN_LAYOUT_H
+
+#include <xen/paging.h>
+#include <xen/sched.h>
+
+/*
+ * Is a domain using the host memory layout?
+ *
+ * domain_use_host_layout() is always False for PV domains (including Dom0).
+ *
+ * Direct-mapped domains (autotranslated domains with memory allocated
+ * contiguously and mapped 1:1 so that GFN == MFN) must use the host
+ * memory layout since GFN == MFN by definition.
+ *
+ * The hardware domain will use the host layout (regardless of
+ * direct-mapped) because some OS may rely on specific address ranges
+ * for the devices.
+ */
+static inline bool domain_use_host_layout(const struct domain *d)
+{
+    return paging_mode_translate(d) &&
+           (is_domain_direct_mapped(d) || is_hardware_domain(d));
+}
+
+#endif /* XEN_DOMAIN_LAYOUT_H */