Merge tag 'x86-mm-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 mm updates from Ingo Molnar:
 "Do not sync vmalloc/ioremap mappings on x86-64 kernels.

  Hopefully now without the bugs!"

* tag 'x86-mm-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/mm/64: Update comment in preallocate_vmalloc_pages()
  x86/mm/64: Do not sync vmalloc/ioremap mappings

Author: torvalds

arch/x86/include/asm/pgtable_64_types.h

@@ -159,6 +159,4 @@ extern unsigned int ptrs_per_p4d;
 
 #define PGD_KERNEL_START	((PAGE_SIZE / 2) / sizeof(pgd_t))
 
-#define ARCH_PAGE_TABLE_SYNC_MASK	(pgtable_l5_enabled() ?	PGTBL_PGD_MODIFIED : PGTBL_P4D_MODIFIED)
-
 #endif /* _ASM_X86_PGTABLE_64_DEFS_H */

arch/x86/mm/init_64.c

@@ -217,11 +217,6 @@ static void sync_global_pgds(unsigned long start, unsigned long end)
 		sync_global_pgds_l4(start, end);
 }
 
-void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
-{
-	sync_global_pgds(start, end);
-}
-
 /*
  * NOTE: This function is marked __ref because it calls __init function
  * (alloc_bootmem_pages). It's safe to do it ONLY when after_bootmem == 0.
@@ -1257,14 +1252,19 @@ static void __init preallocate_vmalloc_pages(void)
 		if (!p4d)
 			goto failed;
 
-		/*
-		 * With 5-level paging the P4D level is not folded. So the PGDs
-		 * are now populated and there is no need to walk down to the
-		 * PUD level.
-		 */
 		if (pgtable_l5_enabled())
 			continue;
 
+		/*
+		 * The goal here is to allocate all possibly required
+		 * hardware page tables pointed to by the top hardware
+		 * level.
+		 *
+		 * On 4-level systems, the P4D layer is folded away and
+		 * the above code does no preallocation.  Below, go down
+		 * to the pud _software_ level to ensure the second
+		 * hardware level is allocated on 4-level systems too.
+		 */
 		lvl = "pud";
 		pud = pud_alloc(&init_mm, p4d, addr);
 		if (!pud)