[PATCH] x86/S3: put data segment registers into known state upon resume

[Jan Beulich <jbeulich@suse.com>]

wakeup_32 sets %ds and %es to BOOT_DS, while leaving %fs at what
wakeup_start did set it to, and %gs at whatever BIOS did load into it.
All of this may end up confusing the first load_segments() to run on
the BSP after resume, in particular allowing a non-nul selector value
to be left in %fs.

Alongside %ss, also put all other data segment registers into the same
state that the boot and CPU bringup paths put them in.

Reported-by: M. Vefa Bicakci <m.v.b@runbox.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/acpi/wakeup_prot.S
+++ b/xen/arch/x86/acpi/wakeup_prot.S
@@ -52,6 +52,16 @@ ENTRY(s3_resume)
         mov     %eax, %ss
         mov     saved_rsp(%rip), %rsp
 
+        /*
+         * Also put other segment registers into known state, like would
+         * be done on the boot path. This is in particular necessary for
+         * the first load_segments() to work as intended.
+         */
+        mov     %eax, %ds
+        mov     %eax, %es
+        mov     %eax, %fs
+        mov     %eax, %gs
+
         /* Reload code selector */
         pushq   $__HYPERVISOR_CS
         leaq    1f(%rip),%rax