x86_64: Reflect new direct mapping region extents in Linux 4.2

Linux commit d52888aa2753 ("x86/mm: Move LDT remap out of KASLR region on
5-level paging") moved direct mapping by one PGD slot to make room for the
LDT remap area. This change has gone mostly unnoticed, because the actual
location of the direct mapping may be randomized with kASLR, so libaddrxlat
was able to find the new address, but there are three caveats:

  1. The upper limit should be extended by 0.5 GiB.
  2. The 4.2 start address should be added to the list of addresses probed
     when establishing a reverse direct map.
  3. The xlat-linux-x86_64-4.13-nover test case specified an impossible
     direct mapping location for that kernel version.

Signed-off-by: Petr Tesarik <[email protected]>

Author: ptesarik

src/addrxlat/x86_64.c

@@ -108,21 +108,30 @@
 /** End of direct physical mapping in Linux between 2.6.11 and 2.6.27 */
 #define LINUX_DIRECTMAP_END_2_6_11	0xffffc0ffffffffff
 
-/** Start of direct physical mapping in Linux 2.6.27+ */
+/** Start of direct physical mapping in Linux between 2.6.27 and 2.6.31 */
 #define LINUX_DIRECTMAP_START_2_6_27	0xffff880000000000
 /** End of direct physical mapping in Linux between 2.6.27 and 2.6.31 */
 #define LINUX_DIRECTMAP_END_2_6_27	0xffffc0ffffffffff
 
-/** Start of direct physical mapping in Linux 2.6.31+ */
+/** Start of direct physical mapping in Linux between 2.6.31 and 4.2 */
 #define LINUX_DIRECTMAP_START_2_6_31	LINUX_DIRECTMAP_START_2_6_27
-/** End of direct physical mapping in Linux 2.6.31+ */
+/** End of direct physical mapping in Linux between 2.6.31 and 4.2 */
 #define LINUX_DIRECTMAP_END_2_6_31	0xffffc7ffffffffff
 
-/** Start of direct physical mapping with 5-level paging */
-#define LINUX_DIRECTMAP_START_5LEVEL	0xff11000000000000
+/** Start of direct physical mapping in Linux 4.2+ */
+#define LINUX_DIRECTMAP_START_4_2	0xffff888000000000
+/** End of direct physical mapping in Linux 4.2+ */
+#define LINUX_DIRECTMAP_END_4_2		0xffffc8ffffffffff
 
-/** End of direct physical mapping with 5-level paging */
-#define LINUX_DIRECTMAP_END_5LEVEL	0xff90ffffffffffff
+/** Start of direct physical mapping with 5-level paging before 4.2 */
+#define LINUX_DIRECTMAP_START_5L	0xff10000000000000
+/** End of direct physical mapping with 5-level paging before 4.2 */
+#define LINUX_DIRECTMAP_END_5L		0xff8fffffffffffff
+
+/** Start of direct physical mapping with 5-level paging in 4.2+ */
+#define LINUX_DIRECTMAP_START_5L_4_2	0xff11000000000000
+/** End of direct physical mapping with 5-level paging in 4.2+ */
+#define LINUX_DIRECTMAP_END_5L_4_2	0xff90ffffffffffff
 
 /** AMD64 (Intel 64) page table step function.
  * @param step  Current step state.
@@ -306,11 +315,11 @@ linux_directmap_by_pgt(struct sys_region *rgn,
 	}
 
 	if (step.meth->param.pgt.pf.nfields == 6) {
-		rgn->first = LINUX_DIRECTMAP_START_5LEVEL;
-		end = LINUX_DIRECTMAP_END_5LEVEL;
+		rgn->first = LINUX_DIRECTMAP_START_5L;
+		end = LINUX_DIRECTMAP_END_5L_4_2;
 	} else {
 		rgn->first = LINUX_DIRECTMAP_START_2_6_31;
-		end = LINUX_DIRECTMAP_END_2_6_31;
+		end = LINUX_DIRECTMAP_END_4_2;
 	}
 	status = lowest_mapped(&step, &rgn->first, end);
 	if (status == ADDRXLAT_OK) {
@@ -408,6 +417,7 @@ linux_rdirect_map(struct os_init_data *ctl)
 	 * Try more recent kernels first.
 	 */
 	static const addrxlat_addr_t fixed_loc[] = {
+		LINUX_DIRECTMAP_START_4_2,
 		LINUX_DIRECTMAP_START_2_6_31,
 		LINUX_DIRECTMAP_START_2_6_11,
 		LINUX_DIRECTMAP_START_2_6_0,

tests/xlat-linux-x86_64-4.13-nover.data

@@ -7,8 +7,9 @@
 00000000250001e1
 # direct mapping (64T)
 @0x25c09880
+0000000000000000
 00000000263cb067*128+1000
-0000000000000000*68
+0000000000000000*67
 @0x263cb000
 80000000000001e3*65536+40000000
 # 2.6.31+ VMEMMAP

tests/xlat-linux-x86_64-4.13-nover.expect

@@ -7,15 +7,15 @@
 
 @direct: LINEAR
   target_as=KPHYSADDR
-  off=0x780000000000
+  off=0x778000000000
 
 @ktext: LINEAR
   target_as=KPHYSADDR
   off=0xa4000000
 
 @rdirect: LINEAR
   target_as=KVADDR
-  off=0xffff880000000000
+  off=0xffff888000000000
 
 @machphys_kphys: LINEAR
   target_as=KPHYSADDR
@@ -33,9 +33,9 @@ ffff800000000000-ffffffffffffffff: @rootpgt
 KV -> PHYS:
 0-7fffffffffff: @rootpgt
 800000000000-ffff7fffffffffff: NONE
-ffff800000000000-ffff87ffffffffff: @rootpgt
-ffff880000000000-ffffc7ffffffffff: @direct
-ffffc80000000000-ffffffff81c08fff: @rootpgt
+ffff800000000000-ffff887fffffffff: @rootpgt
+ffff888000000000-ffffc87fffffffff: @direct
+ffffc88000000000-ffffffff81c08fff: @rootpgt
 ffffffff81c09000-ffffffff81c09fff: @ktext
 ffffffff81c0a000-ffffffffffffffff: @rootpgt