crash_dump: Remove no longer used saved_max_pfn

saved_max_pfn was originally introduced in commit

  92aa63a5 ("[PATCH] kdump: Retrieve saved max pfn")

It used to make sure that the user does not try to read the physical memory
beyond saved_max_pfn. But since commit

  921d58c0 ("vmcore: remove saved_max_pfn check")

it's no longer used for the check. This variable doesn't have any users
anymore so just remove it.

 [ bp: Drop the Calgary IOMMU reference from the commit message. ]
Signed-off-by: Kairui Song <kasong@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Link: https://lkml.kernel.org/r/20200330181544.1595733-1-kasong@redhat.com

arch/x86/kernel/e820.c

@@ -910,14 +910,6 @@ static int __init parse_memmap_one(char *p)
 		return -EINVAL;
 
 	if (!strncmp(p, "exactmap", 8)) {
-#ifdef CONFIG_CRASH_DUMP
-		/*
-		 * If we are doing a crash dump, we still need to know
-		 * the real memory size before the original memory map is
-		 * reset.
-		 */
-		saved_max_pfn = e820__end_of_ram_pfn();
-#endif
 		e820_table->nr_entries = 0;
 		userdef = 1;
 		return 0;

include/linux/crash_dump.h

@@ -97,8 +97,6 @@ extern void unregister_oldmem_pfn_is_ram(void);
 static inline bool is_kdump_kernel(void) { return 0; }
 #endif /* CONFIG_CRASH_DUMP */
 
-extern unsigned long saved_max_pfn;
-
 /* Device Dump information to be filled by drivers */
 struct vmcoredd_data {
 	char dump_name[VMCOREDD_MAX_NAME_BYTES]; /* Unique name of the dump */

kernel/crash_dump.c

@@ -5,12 +5,6 @@
 #include <linux/errno.h>
 #include <linux/export.h>
 
-/*
- * If we have booted due to a crash, max_pfn will be a very low value. We need
- * to know the amount of memory that the previous kernel used.
- */
-unsigned long saved_max_pfn;
-
 /*
  * stores the physical address of elf header of crash image
  *