Revert "arm64: Mark kernel page ranges contiguous"

This reverts commit 348a65cd.

Incorrect page table manipulation that does not respect the ARM ARM
recommended break-before-make sequence may lead to TLB conflicts. The
contiguous PTE patch makes the system even more susceptible to such
errors by changing the mapping from a single page to a contiguous range
of pages. An additional TLB invalidation would reduce the risk window,
however, the correct fix is to switch to a temporary swapper_pg_dir.
Once the correct workaround is done, the reverted commit will be
re-applied.
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>
Reported-by: NJeremy Linton <jeremy.linton@arm.com>

arch/arm64/mm/mmu.c

@@ -85,55 +85,19 @@ static void split_pmd(pmd_t *pmd, pte_t *pte)
 	do {
 		/*
 		 * Need to have the least restrictive permissions available
-		 * permissions will be fixed up later. Default the new page
-		 * range as contiguous ptes.
+		 * permissions will be fixed up later
 		 */
-		set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC_CONT));
+		set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC));
 		pfn++;
 	} while (pte++, i++, i < PTRS_PER_PTE);
 }
 
-/*
- * Given a PTE with the CONT bit set, determine where the CONT range
- * starts, and clear the entire range of PTE CONT bits.
- */
-static void clear_cont_pte_range(pte_t *pte, unsigned long addr)
-{
-	int i;
-
-	pte -= CONT_RANGE_OFFSET(addr);
-	for (i = 0; i < CONT_PTES; i++) {
-		set_pte(pte, pte_mknoncont(*pte));
-		pte++;
-	}
-	flush_tlb_all();
-}
-
-/*
- * Given a range of PTEs set the pfn and provided page protection flags
- */
-static void __populate_init_pte(pte_t *pte, unsigned long addr,
-				unsigned long end, phys_addr_t phys,
-				pgprot_t prot)
-{
-	unsigned long pfn = __phys_to_pfn(phys);
-
-	do {
-		/* clear all the bits except the pfn, then apply the prot */
-		set_pte(pte, pfn_pte(pfn, prot));
-		pte++;
-		pfn++;
-		addr += PAGE_SIZE;
-	} while (addr != end);
-}
-
 static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
-				  unsigned long end, phys_addr_t phys,
+				  unsigned long end, unsigned long pfn,
 				  pgprot_t prot,
 				  void *(*alloc)(unsigned long size))
 {
 	pte_t *pte;
-	unsigned long next;
 
 	if (pmd_none(*pmd) || pmd_sect(*pmd)) {
 		pte = alloc(PTRS_PER_PTE * sizeof(pte_t));
@@ -146,27 +110,9 @@ static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
 
 	pte = pte_offset_kernel(pmd, addr);
 	do {
-		next = min(end, (addr + CONT_SIZE) & CONT_MASK);
-		if (((addr | next | phys) & ~CONT_MASK) == 0) {
-			/* a block of CONT_PTES  */
-			__populate_init_pte(pte, addr, next, phys,
-					    __pgprot(pgprot_val(prot) | PTE_CONT));
-		} else {
-			/*
-			 * If the range being split is already inside of a
-			 * contiguous range but this PTE isn't going to be
-			 * contiguous, then we want to unmark the adjacent
-			 * ranges, then update the portion of the range we
-			 * are interrested in.
-			 */
-			 clear_cont_pte_range(pte, addr);
-			 __populate_init_pte(pte, addr, next, phys, prot);
-		}
-
-		pte += (next - addr) >> PAGE_SHIFT;
-		phys += next - addr;
-		addr = next;
-	} while (addr != end);
+		set_pte(pte, pfn_pte(pfn, prot));
+		pfn++;
+	} while (pte++, addr += PAGE_SIZE, addr != end);
 }
 
 static void split_pud(pud_t *old_pud, pmd_t *pmd)
@@ -227,7 +173,8 @@ static void alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
 				}
 			}
 		} else {
-			alloc_init_pte(pmd, addr, next, phys, prot, alloc);
+			alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
+				       prot, alloc);
 		}
 		phys += next - addr;
 	} while (pmd++, addr = next, addr != end);