x86/mm/64: Do not sync vmalloc/ioremap mappings

Remove the code to sync the vmalloc and ioremap ranges for x86-64. The
page-table pages are all pre-allocated so that synchronization is
no longer necessary.

This is a patch that already went into the kernel as:

	commit 8bb9bf2 ("x86/mm/64: Do not sync vmalloc/ioremap mappings")

But it had to be reverted later because it unveiled a bug from:

	commit 6eb82f9 ("x86/mm: Pre-allocate P4D/PUD pages for vmalloc area")

The bug in that commit causes the P4D/PUD pages not to be correctly
allocated, making the synchronization still necessary. That issue got
fixed meanwhile upstream:

	commit 995909a ("x86/mm/64: Do not dereference non-present PGD entries")

With that fix it is safe again to remove the page-table synchronization
for vmalloc/ioremap ranges on x86-64.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200814151947.26229-2-joro@8bytes.org

Author: joergroedel

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.