ARM: 8988/1: mmu: fix crash in EFI calls due to p4d typo in create_mapping_late()

Commit

  84e6ffb2 ("arm: add support for folded p4d page tables")

updated create_mapping_late() to take folded P4Ds into account when
creating mappings, but inverted the p4d_alloc() failure test, resulting
in no mapping to be created at all.

When the EFI rtc driver subsequently tries to invoke the EFI GetTime()
service, the memory regions covering the EFI data structures are missing
from the page tables, resulting in a crash like

  Unable to handle kernel paging request at virtual address 5ae0cf28
  pgd = (ptrval)
  [5ae0cf28] *pgd=80000040205003, *pmd=00000000
  Internal error: Oops: 207 [#1] SMP THUMB2
  Modules linked in:
  CPU: 0 PID: 7 Comm: kworker/u32:0 Not tainted 5.7.0+ #92
  Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
  Workqueue: efi_rts_wq efi_call_rts
  PC is at efi_call_rts+0x94/0x294
  LR is at efi_call_rts+0x83/0x294
  pc : [<c0b4f098>]    lr : [<c0b4f087>]    psr: 30000033
  sp : e6219ef0  ip : 00000000  fp : ffffe000
  r10: 00000000  r9 : 00000000  r8 : 30000013
  r7 : e6201dd0  r6 : e6201ddc  r5 : 00000000  r4 : c181f264
  r3 : 5ae0cf10  r2 : 00000001  r1 : e6201dd0  r0 : e6201ddc
  Flags: nzCV  IRQs on  FIQs on  Mode SVC_32  ISA Thumb  Segment none
  Control: 70c5383d  Table: 661cc840  DAC: 00000001
  Process kworker/u32:0 (pid: 7, stack limit = 0x(ptrval))
  ...
  [<c0b4f098>] (efi_call_rts) from [<c0448219>] (process_one_work+0x16d/0x3d8)
  [<c0448219>] (process_one_work) from [<c0448581>] (worker_thread+0xfd/0x408)
  [<c0448581>] (worker_thread) from [<c044ca7b>] (kthread+0x103/0x104)
  ...

Fixes: 84e6ffb2 ("arm: add support for folded p4d page tables")
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

arch/arm/mm/mmu.c

@@ -966,7 +966,7 @@ void __init create_mapping_late(struct mm_struct *mm, struct map_desc *md,
 	pud_t *pud;
 
 	p4d = p4d_alloc(mm, pgd_offset(mm, md->virtual), md->virtual);
-	if (!WARN_ON(!p4d))
+	if (WARN_ON(!p4d))
 		return;
 	pud = pud_alloc(mm, p4d, md->virtual);
 	if (WARN_ON(!pud))