Commit 23b2a4dd authored Mar 22, 2017 by Andy Lutomirski Committed by Ingo Molnar Mar 23, 2017

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



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.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Garnier <thgarnie@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/a553264a5972c6a86f9b5caac237470a0c74a720.1490218061.git.luto@kernel.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 3fa1cabb

arch/x86/kernel/setup.c

+0 −15

Original line number	Diff line number	Diff line
		@@ -1226,21 +1226,6 @@ 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();

arch/x86/kernel/setup_percpu.c

+21 −0

Original line number	Diff line number	Diff line
		@@ -288,4 +288,25 @@ 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
		}

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