[PATCH V2] xen/arm: Initialize acpi_disabled to true during declaration

[Oleksandr Tyshchenko <Oleksandr_Tyshchenko@xxxxxxxx>]

On the device-tree-based Arm64 system, if Xen is built with
CONFIG_ACPI=y, CONFIG_STATIC_MEMORY=y, and the static memory range
is provided in the host device tree, the BUG is triggered in
common/page_alloc.c during Xen's early boot. The BUG occurs when
the first page from the static range is fed to the domain
sub-allocator and finally ends up in mark_page_free().
The pg->count_info & PGC_state is not in the state that
the code expects to see there.

(XEN) Checking for initrd in /chosen
(XEN) Checking for "xen,static-mem" in domain node
(XEN) RAM: 0000000040000000 - 00000000bfffffff
(XEN)
(XEN) MODULE[0]: 0000000043200000 - 0000000043343fff Xen
(XEN) MODULE[1]: 0000000043400000 - 0000000043402fff Device Tree
(XEN) MODULE[2]: 0000000042e00000 - 0000000043111f82 Ramdisk
(XEN) MODULE[3]: 0000000040400000 - 0000000042cfffff Kernel
(XEN)  RESVD[0]: 0000000050000000 - 000000005fffffff
(XEN)
(XEN) CMDLINE[0000000040400000]:domU0 console=ttyAMA0
(XEN)
(XEN) Command line: console=dtuart conswitch=ax
(XEN) pg MFN 50000 c=0x2180000000000000 o=0 v=0 t=0
(XEN) Xen BUG at common/page_alloc.c:1474
[snip]

The problem is that the static range gets mistakenly unreserved
in populate_boot_allocator() and reaches init_boot_pages().
This happens since by the time the populate_boot_allocator()
is executed, the evaluated in fw_unreserved_regions()
an acpi_disabled variable is still false and as the result
the dt_unreserved_regions() which should simply skip that static range
does not get called. The acpi_disabled will be set to the actual value
(in our case it is true) later on in acpi_boot_table_init().

The important question is why acpi_disabled is false by the time
setup_mm() is executed. With CONFIG_ACPI=n it is a macro that is always
true, but with CONFIG_ACPI=y it is a boolean that is false from the very
beggining, even though the entire acpi_boot_table_init() (which is called
after setup_mm()) is written with the assumption that ACPI is off by default
at the start. So, initialize acpi_disabled to true during declaration
if CONFIG_ACPI=y to avoid an issue and match to acpi_boot_table_init().

Suggested-by: Michal Orzel <michal.orzel@xxxxxxx>
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
---
  V2:
   - drop post-commit remark
   - use the approach suggested by Michal
   - update commit subject (WAS xen/device-tree: Switch back to 
dt_unreserved_regions() in boot allocator)
     and description
---
---
 xen/arch/arm/setup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index ffcae900d7..9e94f1a8c7 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -57,7 +57,7 @@
 struct cpuinfo_arm __read_mostly system_cpuinfo;
 
 #ifdef CONFIG_ACPI
-bool __read_mostly acpi_disabled;
+bool __read_mostly acpi_disabled = true;
 #endif
 
 domid_t __read_mostly max_init_domid;
-- 
2.34.1