Patch "x86/boot/32: Defer resyncing initial_page_table until per-cpu is set up" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

x86/boot/32: Defer resyncing initial_page_table until per-cpu is set up

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-boot-32-defer-resyncing-initial_page_table-until-per-cpu-is-set-up.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andy Lutomirski <[email protected]>
Date: Wed, 22 Mar 2017 14:32:32 -0700
Subject: x86/boot/32: Defer resyncing initial_page_table until per-cpu is set up

From: Andy Lutomirski <[email protected]>

[ Upstream commit 23b2a4ddebdd17fad265b4bb77256c2e4ec37dee ]

The x86 smpboot trampoline expects initial_page_table to have the GDT mapped. If the GDT ends up in a virtually mapped per-cpu page, then it won't be in the page tables at all until perc-pu areas are set up. The result will be a triple fault the first time that the CPU attempts to access the GDT after LGDT loads the perc-pu GDT.

This appears to be an old bug, but somehow the GDT fixmap rework is triggering it. This seems to have something to do with the memory layout.

---
 arch/x86/kernel/setup.c        |   15 ---------------
 arch/x86/kernel/setup_percpu.c |   21 +++++++++++++++++++++
 2 files changed, 21 insertions(+), 15 deletions(-)

@@ -1200,21 +1200,6 @@ void __init setup_arch(char **cmdline_p)
 
 	kasan_init();
 
-#ifdef CONFIG_X86_32
-	/* sync back kernel address range */
-	clone_pgd_range(initial_page_table + KERNEL_PGD_BOUNDARY,
-			swapper_pg_dir     + KERNEL_PGD_BOUNDARY,
-			KERNEL_PGD_PTRS);
-
-	/*
-	 * sync back low identity map too.  It is used for example
-	 * in the 32-bit EFI stub.
-	 */
-	clone_pgd_range(initial_page_table,
-			swapper_pg_dir     + KERNEL_PGD_BOUNDARY,
-			min(KERNEL_PGD_PTRS, KERNEL_PGD_BOUNDARY));
-#endif
-
 	tboot_probe();
 
 	map_vsyscall();

@@ -287,4 +287,25 @@ void __init setup_per_cpu_areas(void)
 
 	/* Setup cpu initialized, callin, callout masks */
 	setup_cpu_local_masks();
+
+#ifdef CONFIG_X86_32
+	/*
+	 * Sync back kernel address range.  We want to make sure that
+	 * all kernel mappings, including percpu mappings, are available
+	 * in the smpboot asm.  We can't reliably pick up percpu
+	 * mappings using vmalloc_fault(), because exception dispatch
+	 * needs percpu data.
+	 */
+	clone_pgd_range(initial_page_table + KERNEL_PGD_BOUNDARY,
+			swapper_pg_dir     + KERNEL_PGD_BOUNDARY,
+			KERNEL_PGD_PTRS);
+
+	/*
+	 * sync back low identity map too.  It is used for example
+	 * in the 32-bit EFI stub.
+	 */
+	clone_pgd_range(initial_page_table,
+			swapper_pg_dir     + KERNEL_PGD_BOUNDARY,
+			min(KERNEL_PGD_PTRS, KERNEL_PGD_BOUNDARY));
+#endif
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/perf-tools-make-perf_event__synthesize_mmap_events-scale.patch queue-4.9/x86-mm-make-mmap-map_32bit-work-correctly.patch queue-4.9/x86-boot-32-defer-resyncing-initial_page_table-until-per-cpu-is-set-up.patch

On Mar 18, 2018, at 9:06 AM, <[email protected]> <[email protected]> wrote:

This is a note to let you know that I've just added the patch titled

x86/boot/32: Defer resyncing initial_page_table until per-cpu is set up

Please make sure you get “x86/boot/32: Fix UP boot on Quark and possibly other platforms” too. Sorry, the fixes tag is missing.

Thanks for the info, that patch is now queued up.

greg k-h