arm64/mm: Drop redundant BUG_ON(!pgtable_alloc)

__create_pgd_mapping_locked() expects a page allocator used while mapping a
virtual range. This page allocator function propagates down the call chain,
while building intermediate levels in the page table. Passed page allocator
is a necessary ingredient required to build the page table but its presence
can be asserted just once in the very beginning rather than in all the down
stream functions. This consolidates BUG_ON(!pgtable_alloc) checks just in a
single place i.e __create_pgd_mapping_locked().

Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Anshuman Khandual <[email protected]>
Acked-by: Mark Rutland <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

Author: Anshuman Khandual

arch/arm64/mm/mmu.c

@@ -207,7 +207,6 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
 
 		if (flags & NO_EXEC_MAPPINGS)
 			pmdval |= PMD_TABLE_PXN;
-		BUG_ON(!pgtable_alloc);
 		pte_phys = pgtable_alloc(PAGE_SHIFT);
 		__pmd_populate(pmdp, pte_phys, pmdval);
 		pmd = READ_ONCE(*pmdp);
@@ -285,7 +284,6 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
 
 		if (flags & NO_EXEC_MAPPINGS)
 			pudval |= PUD_TABLE_PXN;
-		BUG_ON(!pgtable_alloc);
 		pmd_phys = pgtable_alloc(PMD_SHIFT);
 		__pud_populate(pudp, pmd_phys, pudval);
 		pud = READ_ONCE(*pudp);
@@ -324,7 +322,6 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
 
 		if (flags & NO_EXEC_MAPPINGS)
 			p4dval |= P4D_TABLE_PXN;
-		BUG_ON(!pgtable_alloc);
 		pud_phys = pgtable_alloc(PUD_SHIFT);
 		__p4d_populate(p4dp, pud_phys, p4dval);
 		p4d = READ_ONCE(*p4dp);
@@ -383,6 +380,7 @@ static void __create_pgd_mapping_locked(pgd_t *pgdir, phys_addr_t phys,
 	phys &= PAGE_MASK;
 	addr = virt & PAGE_MASK;
 	end = PAGE_ALIGN(virt + size);
+	BUG_ON(!pgtable_alloc);
 
 	do {
 		next = pgd_addr_end(addr, end);