Revert "x86, mm: Include the entire kernel memory map in trampoline_pgd"

This reverts commit 53b87cf088e2ea68d7c59619d0214cc15bb76133.

It causes odd bootup problems on x86-64.  Markus Trippelsdorf gets a
repeatable oops, and I see a non-repeatable oops (or constant stream of
messages that scroll off too quickly to read) that seems to go away with
this commit reverted.

So we don't know exactly what is wrong with the commit, but it's
definitely problematic, and worth reverting sooner rather than later.

Bisected-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: H Peter Anvin <hpa@zytor.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 15 deletions

diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index 8e6ab6137852..cbca565af5bd 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -78,21 +78,8 @@ void __init setup_real_mode(void)
 	*trampoline_cr4_features = read_cr4();
 
 	trampoline_pgd = (u64 *) __va(real_mode_header->trampoline_pgd);
-
-	/*
-	 * Create an identity mapping for all of physical memory.
-	 */
-	for (i = 0; i <= pgd_index(max_pfn << PAGE_SHIFT); i++) {
-		int index = pgd_index(PAGE_OFFSET) + i;
-
-		trampoline_pgd[i] = (u64)pgd_val(swapper_pg_dir[index]);
-	}
-
-	/*
-	 * Copy the upper-half of the kernel pages tables.
-	 */
-	for (i = pgd_index(PAGE_OFFSET); i < PTRS_PER_PGD; i++)
-		trampoline_pgd[i] = (u64)pgd_val(swapper_pg_dir[i]);
+	trampoline_pgd[0] = __pa(level3_ident_pgt) + _KERNPG_TABLE;
+	trampoline_pgd[511] = __pa(level3_kernel_pgt) + _KERNPG_TABLE;
 #endif
 }