powerpc/kdump: Fix size calculation for hot-removed memory ranges

The elfcorehdr segment in the kdump image stores information about the
memory regions (called crash memory ranges) that the kdump kernel must
capture.

When a memory hot-remove event occurs, the kernel regenerates the
elfcorehdr for the currently loaded kdump image to remove the
hot-removed memory from the crash memory ranges.

Call chain:
remove_mem_range()
update_crash_elfcorehdr()
arch_crash_handle_hotplug_event()
crash_handle_hotplug_event()

While removing the hot-removed memory from the crash memory ranges in
remove_mem_range(), if the removed memory lies within an existing crash
range, that range is split into two. During this split, the size of the
second range was being calculated incorrectly.

This leads to dump capture failure with makedumpfile with below error:

$ makedumpfile -l -d 31 /proc/vmcore /tmp/vmcore

readpage_elf: Attempt to read non-existent page at 0xbbdab0000.
readmem: type_addr: 0, addr:c000000bbdab7f00, size:16
validate_mem_section: Can't read mem_section array.
readpage_elf: Attempt to read non-existent page at 0xbbdab0000.
readmem: type_addr: 0, addr:c000000bbdab7f00, size:8
get_mm_sparsemem: Can't get the address of mem_section.

The updated crash memory range in PT_LOAD entry is holding incorrect
data (checkout FileSiz and MemSiz):

readelf -a /proc/vmcore
<snip...>
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000b013d0000 0xc000000b80000000 0x0000000b80000000
0xffffffffc0000000 0xffffffffc0000000 RWE 0x0
<snip...>

Update the size calculation for the new crash memory range to fix this
issue.

Note: This problem will not occur if the kdump kernel is loaded or
reloaded after a memory hot-remove operation.

Fixes: 849599b702ef ("powerpc/crash: add crash memory hotplug support")
Reported-by: Shirisha G <[e-mail]>
Signed-off-by: Sourabh Jain <[e-mail]>
Signed-off-by: Madhavan Srinivasan <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

arch/powerpc/kexec/ranges.c

···
 		 * two half.
 		 */
 		else {
+			size = mem_rngs->ranges[i].end - end + 1;
 			mem_rngs->ranges[i].end = base - 1;
-			size = mem_rngs->ranges[i].end - end;
 			ret = add_mem_range(mem_ranges, end + 1, size);
 		}
 	}