[Crash-utility] [PATCH v2] x86_64: Make the conversion between 4level and 5level paging automatically

[Dou Liyang]

Currently, Crash only enable support for kernel-only 5-level page tables by
entering the command line option "--machdep vm=5level". Since Linux 4.17,
the Linux kernel can be both 4level and 5level page tables. This command line
can't work well for this.

Using the "pgtable_l5_enabled" to detect whether the kernel proper for 5 level
page tables automatically. Also move the 5-level paging setup from machdep_init(PRE_GDB)
to machdep_init(POST_RELOC).

Signed-off-by: Dave Anderson <anderson at redhat.com>
Signed-off-by: Dou Liyang <douly.fnst at cn.fujitsu.com>
---
Changelog v1 --> v2

 1. Make it support live systems suggested by Dave
 2. Using __pgtable_l5_enabled for check.
 3. Do some tests in both kdump(5level and 4level) and virsh dump(5level and 4level) 
---
 x86_64.c | 56 +++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 37 insertions(+), 19 deletions(-)

diff --git a/x86_64.c b/x86_64.c
index 6d1ae2f..07b6aa9 100644
--- a/x86_64.c
+++ b/x86_64.c
@@ -294,25 +294,6 @@ x86_64_init(int when)
 			machdep->machspec->pgdir_shift = PGDIR_SHIFT;
 			machdep->machspec->ptrs_per_pgd = PTRS_PER_PGD;
 			break;
-
-		case VM_5LEVEL:
-			machdep->machspec->userspace_top = USERSPACE_TOP_5LEVEL;
-			machdep->machspec->page_offset = PAGE_OFFSET_5LEVEL;
-			machdep->machspec->vmalloc_start_addr = VMALLOC_START_ADDR_5LEVEL;
-			machdep->machspec->vmalloc_end = VMALLOC_END_5LEVEL;
-			machdep->machspec->modules_vaddr = MODULES_VADDR_5LEVEL;
-			machdep->machspec->modules_end = MODULES_END_5LEVEL;
-			machdep->machspec->vmemmap_vaddr = VMEMMAP_VADDR_5LEVEL;
-			machdep->machspec->vmemmap_end = VMEMMAP_END_5LEVEL;
-			if (symbol_exists("vmemmap_populate"))
-				machdep->flags |= VMEMMAP;
-			machdep->machspec->physical_mask_shift = __PHYSICAL_MASK_SHIFT_5LEVEL;
-			machdep->machspec->pgdir_shift = PGDIR_SHIFT_5LEVEL;
-			machdep->machspec->ptrs_per_pgd = PTRS_PER_PGD_5LEVEL;
-			if ((machdep->machspec->p4d = (char *)malloc(PAGESIZE())) == NULL)
-				error(FATAL, "cannot malloc p4d space.");
-			machdep->machspec->last_p4d_read = 0;
-			machdep->uvtop = x86_64_uvtop_level4;  /* 5-level is optional per-task */
 		}
 	        machdep->kvbase = (ulong)PAGE_OFFSET;
 		machdep->identity_map_base = (ulong)PAGE_OFFSET;
@@ -346,6 +327,43 @@ x86_64_init(int when)
 		break;
 
 	case POST_RELOC:
+		/* Check for 5-level paging */
+		if (!(machdep->flags & VM_5LEVEL)) {
+			int l5_enabled;
+			if ((string = pc->read_vmcoreinfo("NUMBER(pgtable_l5_enabled)"))) {
+				l5_enabled = 1;
+				free(string);
+			} else if (kernel_symbol_exists("__pgtable_l5_enabled"))
+				readmem(symbol_value("__pgtable_l5_enabled"), KVADDR,
+					&l5_enabled, sizeof(int), "__pgtable_l5_enabled",
+					FAULT_ON_ERROR);
+
+			if (l5_enabled)
+				machdep->flags |= VM_5LEVEL;
+		}
+		if (machdep->flags & VM_5LEVEL) {
+			machdep->machspec->userspace_top = USERSPACE_TOP_5LEVEL;
+			machdep->machspec->page_offset = PAGE_OFFSET_5LEVEL;
+			machdep->machspec->vmalloc_start_addr = VMALLOC_START_ADDR_5LEVEL;
+			machdep->machspec->vmalloc_end = VMALLOC_END_5LEVEL;
+			machdep->machspec->modules_vaddr = MODULES_VADDR_5LEVEL;
+			machdep->machspec->modules_end = MODULES_END_5LEVEL;
+			machdep->machspec->vmemmap_vaddr = VMEMMAP_VADDR_5LEVEL;
+			machdep->machspec->vmemmap_end = VMEMMAP_END_5LEVEL;
+			if (symbol_exists("vmemmap_populate"))
+				machdep->flags |= VMEMMAP;
+			machdep->machspec->physical_mask_shift = __PHYSICAL_MASK_SHIFT_5LEVEL;
+			machdep->machspec->pgdir_shift = PGDIR_SHIFT_5LEVEL;
+			machdep->machspec->ptrs_per_pgd = PTRS_PER_PGD_5LEVEL;
+			if ((machdep->machspec->p4d = (char *)malloc(PAGESIZE())) == NULL)
+				error(FATAL, "cannot malloc p4d space.");
+			machdep->machspec->last_p4d_read = 0;
+			machdep->uvtop = x86_64_uvtop_level4;  /* 5-level is optional per-task */
+			machdep->kvbase = (ulong)PAGE_OFFSET;
+			machdep->identity_map_base = (ulong)PAGE_OFFSET;
+
+		}
+
 		/*
 		 *  Check for CONFIG_RANDOMIZE_MEMORY, and set page_offset here.
 		 *  The remainder of the virtual address range setups will get
-- 
2.14.3