arm64/mm: add create_pgd_mapping() to create private page tables

For UEFI, we need to install the memory mappings used for Runtime Services
in a dedicated set of page tables. Add create_pgd_mapping(), which allows
us to allocate and install those page table entries early.

Reviewed-by: Will Deacon <will.deacon@arm.com>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

arch/arm64/include/asm/mmu.h

@@ -33,5 +33,8 @@ extern void __iomem *early_io_map(phys_addr_t phys, unsigned long virt);
 extern void init_mem_pgprot(void);
 /* create an identity mapping for memory (or io if map_io is true) */
 extern void create_id_mapping(phys_addr_t addr, phys_addr_t size, int map_io);
+extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
+			       unsigned long virt, phys_addr_t size,
+			       pgprot_t prot);
 
 #endif