Currently, only the whole physical memory is identity-mapped for the
kexec kernel and the regions reserved by firmware are ignored.

However, the recent addition of RSDP parsing in the decompression stage
and especially:

  33f0df8d ("x86/boot: Search for RSDP in the EFI tables")

which tries to access EFI system tables and to dig out the RDSP address
from there, becomes a problem because in certain configurations, they
might not be mapped in the kexec'ed kernel's address space.

What is more, this problem doesn't appear on all systems because the
kexec kernel uses gigabyte pages to build the identity mapping. And
the EFI system tables and ACPI tables can, depending on the system
configuration, end up being mapped as part of all physical memory, if
they share the same 1 GB area with the physical memory.

Therefore, make sure they're always mapped.

 [ bp: productize half-baked patch:
   - rewrite commit message.
   - correct the map_acpi_tables() function name in the !ACPI case. ]
Signed-off-by: Kairui Song <kasong@redhat.com>
Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Cc: dyoung@redhat.com
Cc: fanc.fnst@cn.fujitsu.com
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: j-nomura@ce.jp.nec.com
Cc: kexec@lists.infradead.org
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Lianbo Jiang <lijiang@redhat.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190429002318.GA25400@MiWiFi-R3L-srv