xen/arm: Allow the user to build Xen with UBSAN

UBSAN has been enabled a few years ago on x86 but was never
enabled on Arm because the final binary is bigger than 2MB (
the maximum we can currently handled).

With the recent rework, it is now possible to grow Xen over 2MB.
So there is no more roadblock to enable Xen other than increasing
the reserved area.

On my setup, for arm32, the final binaray was very close to 4MB.
Furthermore, one may want to enable UBSAN and GCOV which would put
the binary well-over 4MB (both features require for some space).
Therefore, increase the size to 8MB which should us some margin.

Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Henry Wang <Henry.Wang@arm.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>o

xen/arch/arm/Kconfig

@@ -17,6 +17,7 @@ config ARM
 	select HAS_PASSTHROUGH
 	select HAS_PDX
 	select HAS_PMAP
+	select HAS_UBSAN
 	select IOMMU_FORCE_PT_SHARE
 
 config ARCH_DEFCONFIG

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

@@ -74,10 +74,10 @@
 /*
  * ARM32 layout:
  *   0  -   2M   Unmapped
- *   2M -   4M   Xen text, data, bss
- *   4M -   6M   Fixmap: special-purpose 4K mapping slots
- *   6M -  10M   Early boot mapping of FDT
- *   10M - 12M   Livepatch vmap (if compiled in)
+ *   2M -  10M   Xen text, data, bss
+ *  10M -  12M   Fixmap: special-purpose 4K mapping slots
+ *  12M -  16M   Early boot mapping of FDT
+ *  16M -  18M   Livepatch vmap (if compiled in)
  *
  *  32M - 128M   Frametable: 32 bytes per page for 12GB of RAM
  * 256M -   1G   VMAP: ioremap and early_ioremap use this virtual address
@@ -94,10 +94,10 @@
  * 0x0000020000000000 - 0x0000027fffffffff (512GB, L0 slot [4])
  *  (Relative offsets)
  *   0  -   2M   Unmapped
- *   2M -   4M   Xen text, data, bss
- *   4M -   6M   Fixmap: special-purpose 4K mapping slots
- *   6M -  10M   Early boot mapping of FDT
- *  10M -  12M   Livepatch vmap (if compiled in)
+ *   2M -  10M   Xen text, data, bss
+ *  10M -  12M   Fixmap: special-purpose 4K mapping slots
+ *  12M -  16M   Early boot mapping of FDT
+ *  16M -  18M   Livepatch vmap (if compiled in)
  *
  *   1G -   2G   VMAP: ioremap and early_ioremap
  *
@@ -124,7 +124,11 @@
 #define XEN_VIRT_START          (SLOT0(4) + _AT(vaddr_t, MB(2)))
 #endif
 
-#define XEN_VIRT_SIZE           _AT(vaddr_t, MB(2))
+/*
+ * Reserve enough space so both UBSAN and GCOV can be enabled together
+ * plus some slack for future growth.
+ */
+#define XEN_VIRT_SIZE           _AT(vaddr_t, MB(8))
 #define XEN_NR_ENTRIES(lvl)     (XEN_VIRT_SIZE / XEN_PT_LEVEL_SIZE(lvl))
 
 #define FIXMAP_VIRT_START       (XEN_VIRT_START + XEN_VIRT_SIZE)