arm64: implement switchable PTOV()/VTOP() for kernels >= 5.10

Crash encounters a bug like the following:
    ...
    SECTION_SIZE_BITS: 30
    CONFIG_ARM64_VA_BITS: 52
          VA_BITS_ACTUAL: 48
    (calculated) VA_BITS: 48
     PAGE_OFFSET: ffff000000000000
        VA_START: ffff800000000000
         modules: ffff800008000000 - ffff80000fffffff
         vmalloc: ffff800010000000 - ffffffdfdffeffff
    kernel image: ffff800010000000 - ffff800012750000
         vmemmap: ffffffdfffe00000 - ffffffffffffffff

    <readmem: ffff800011c53bc8, KVADDR, "nr_irqs", 4, (FOE), b47bdc>
    <read_kdump: addr: ffff800011c53bc8 paddr: eb453bc8 cnt: 4>
    read_netdump: addr: ffff800011c53bc8 paddr: eb453bc8 cnt: 4 offset: 1c73bc8
    irq_stack_ptr:
      type: 1, TYPE_CODE_PTR
      target_typecode: 8, TYPE_CODE_INT
      target_length: 8
      length: 8
    GNU_GET_DATATYPE[thread_union]: returned via gdb_error_hook
    <readmem: ffff000b779c0050, KVADDR, "IRQ stack pointer", 8, (ROE), 3a37bea0>
    <read_kdump: addr: ffff000b779c0050 paddr: fff1000bf79c0050 cnt: 8>
    read_netdump: READ_ERROR: offset not found for paddr: fff1000bf79c0050
    crash: read error: kernel virtual address: ffff000b779c0050  type: "IRQ stack pointer"
    ...

Apparently, for a normal system, the 'paddr: fff1000bf79c0050' is
unreasonable.

This bug connects with kernel commit 7bc1a0f9e176 ("arm64: mm: use
single quantity to represent the PA to VA translation"), which removed
physvirt_offset kernel variable and changed the PTOV()/VTOP() formulas.

Implement switchable PTOV()/VTOP() to cope with different kernel
version.

Signed-off-by: Pingfan Liu <piliu@redhat.com>

arm64.c

@@ -994,17 +994,20 @@ arm64_calc_physvirt_offset(void)
 	ulong physvirt_offset;
 	struct syment *sp;
 
-	ms->physvirt_offset = ms->phys_offset - ms->page_offset;
-
 	if ((sp = kernel_symbol_search("physvirt_offset")) &&
 			machdep->machspec->kimage_voffset) {
 		if (READMEM(pc->mfd, &physvirt_offset, sizeof(physvirt_offset),
 			sp->value, sp->value -
 			machdep->machspec->kimage_voffset) > 0) {
 				machdep->flags |= HAS_PHYSVIRT_OFFSET;
 				ms->physvirt_offset = physvirt_offset;
+				return;
 		}
 	}
+
+	/* Useless if no symbol 'physvirt_offset', just keep semantics */
+	ms->physvirt_offset = ms->phys_offset - ms->page_offset;
+
 }
 
 static void
@@ -1051,6 +1054,7 @@ arm64_calc_phys_offset(void)
 			if (READMEM(pc->mfd, &phys_offset, sizeof(phys_offset),
 			    vaddr, paddr) > 0) {
 				ms->phys_offset = phys_offset;
+
 				return;
 			}
 		}
@@ -1178,6 +1182,21 @@ arm64_init_kernel_pgd(void)
                 vt->kernel_pgd[i] = value;
 }
 
+ulong arm64_PTOV(ulong paddr)
+{
+	struct machine_specific *ms = machdep->machspec;
+
+	/*
+	 * Either older kernel before kernel has 'physvirt_offset' or newer
+	 * kernel which removes 'physvirt_offset' has the same formula:
+	 * #define __phys_to_virt(x)   ((unsigned long)((x) - PHYS_OFFSET) | PAGE_OFFSET)
+	 */
+	if (!(machdep->flags & HAS_PHYSVIRT_OFFSET))
+		return (paddr - ms->phys_offset) | PAGE_OFFSET;
+	else
+		return paddr - ms->physvirt_offset;
+}
+
 ulong
 arm64_VTOP(ulong addr)
 {
@@ -1188,8 +1207,18 @@ arm64_VTOP(ulong addr)
 			return addr - machdep->machspec->kimage_voffset;
 		}
 
-		if (addr >= machdep->machspec->page_offset)
-			return addr + machdep->machspec->physvirt_offset;
+		if (addr >= machdep->machspec->page_offset) {
+			if (machdep->flags & HAS_PHYSVIRT_OFFSET) {
+				return addr + machdep->machspec->physvirt_offset;
+			} else {
+				/*
+				 * Either older kernel before kernel has 'physvirt_offset' or newer
+				 * kernel which removes 'physvirt_offset' has the same formula:
+				 * #define __lm_to_phys(addr)	(((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
+				 */
+				return (addr & ~PAGE_OFFSET) + machdep->machspec->phys_offset;
+			}
+		}
 		else if (machdep->machspec->kimage_voffset)
 			return addr - machdep->machspec->kimage_voffset;
 		else /* no randomness */

defs.h

@@ -3092,11 +3092,6 @@ typedef u64 pte_t;
 #define _64BIT_
 #define MACHINE_TYPE       "ARM64"    
 
-#define PTOV(X) \
-	((unsigned long)(X) - (machdep->machspec->physvirt_offset))
-
-#define VTOP(X)               arm64_VTOP((ulong)(X))
-
 #define USERSPACE_TOP   (machdep->machspec->userspace_top)
 #define PAGE_OFFSET     (machdep->machspec->page_offset)
 #define VMALLOC_START   (machdep->machspec->vmalloc_start_addr)
@@ -3106,6 +3101,9 @@ typedef u64 pte_t;
 #define MODULES_VADDR   (machdep->machspec->modules_vaddr)
 #define MODULES_END     (machdep->machspec->modules_end)
 
+#define PTOV(X)	arm64_PTOV((ulong)(X))
+#define VTOP(X)	arm64_VTOP((ulong)(X))
+
 #define IS_VMALLOC_ADDR(X)    arm64_IS_VMALLOC_ADDR((ulong)(X))
 
 #define PAGEBASE(X)     (((ulong)(X)) & (ulong)machdep->pagemask)
@@ -5910,6 +5908,7 @@ void unwind_backtrace(struct bt_info *);
 void arm64_init(int);
 void arm64_dump_machdep_table(ulong);
 ulong arm64_VTOP(ulong);
+ulong arm64_PTOV(ulong);
 int arm64_IS_VMALLOC_ADDR(ulong);
 ulong arm64_swp_type(ulong);
 ulong arm64_swp_offset(ulong);