Fix domain pickled_id computation for xen-3.4+

Originally, Xen stored the 32-bit address of the domain structure in struct page_info. On x86-64, the physical address was stored, but since all heap objects were allocated in the 1:1 mapping which started at 0xffff830000000000, the end result was the same as if we simply chopped off the high bits (actual implementation in makedumpfile).

Then, during the development of Xen-3.4, this logic was changed several times for x86-64:

changeset 39517e863cc8 widened the _domain field to 64 bits and stored the
virtual address of struct domain instead of physical address
changeset beba88f6f90d removed the pickle/unpickle macros changeset 0858f961c77a changed _domain back from unsigned long to u32,
*and* stores the MFN of struct domain instead

All the above changes went into Xen-3.4, and the relation between a domain address and the contents of the _domain field hasn't changed since then. That means, when the MADDR space was compressed in Xen-4.0, the type of the _domain field was changed to _pdx_t, which was specifically invented to preserve its calculation from the struct domain address.

To sum it up:

1. For all Xen versions before Xen-3.4, the _domain field contains the address of struct domain (with high bits chopped for x86-64).
2. For all Xen versions starting with Xen-3.4, the _domain field can be computed from struct domain address as:
(addr - DIRECTMAP_VIRT_START) >> PAGE_SHIFT

---
 arch/x86_64.c |   26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

@@ -405,12 +405,26 @@ int get_xen_info_x86_64(void)
 {
 	int i;
 
-	/*
-	 * pickled_id == domain addr for x86_64
-	 */
-	for (i = 0; i < info->num_domain; i++) {
-		info->domain_list[i].pickled_id =
-			info->domain_list[i].domain_addr;
+	if (info->xen_crash_info.com &&
+	    (info->xen_crash_info.com->xen_major_version >= 4 ||
+	     (info->xen_crash_info.com->xen_major_version == 3 &&
+	      info->xen_crash_info.com->xen_minor_version >= 4))) {
+		/*
+		 * cf. changeset 0858f961c77a
+		 */
+		for (i = 0; i < info->num_domain; i++) {
+			info->domain_list[i].pickled_id =
+				(info->domain_list[i].domain_addr -
+				 DIRECTMAP_VIRT_START) >> PAGESHIFT();
+		}
+	} else {
+		/*
+		 * pickled_id == domain addr for x86_64
+		 */
+		for (i = 0; i < info->num_domain; i++) {
+			info->domain_list[i].pickled_id =
+				info->domain_list[i].domain_addr;
+		}
 	}
 
 	return TRUE;

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