Re: [PATCH] x86: fix CONFIG_VMSPLIT_1G and 2G_OPT trampoline

From: Borislav Petkov
Date: Wed Aug 25 2010 - 02:34:52 EST


From: Hugh Dickins <hughd@xxxxxxxxxx>
Date: Wed, Aug 25, 2010 at 01:44:12AM -0400

> rc2 kernel crashes when booting second cpu on this CONFIG_VMSPLIT_2G_OPT
> laptop: whereas cloning from kernel to low mappings pgd range does need
> to limit by both KERNEL_PGD_PTRS and KERNEL_PGD_BOUNDARY, cloning kernel
> pgd range itself must not be limited by the smaller KERNEL_PGD_BOUNDARY.

Yep, makes sense.

In looking around for other swapper_pg_dir manipulations, there's this
piece in <arch/x86/kernel/reboot.c:machine_real_restart()>:

/* Remap the kernel at virtual address zero, as well as offset zero
from the kernel segment. This assumes the kernel segment starts at
virtual address PAGE_OFFSET. */
memcpy(swapper_pg_dir, swapper_pg_dir + KERNEL_PGD_BOUNDARY,
sizeof(swapper_pg_dir [0]) * KERNEL_PGD_PTRS);

and we're cloning to low mappings here but still take KERNEL_PGD_PTRS.

In the CONFIG_VMSPLIT_2G_OPT case, KERNEL_PGD_BOUNDARY and
KERNEL_PGD_PTRS are 480 and 544, respectively, and IINM, and we end up
overwriting the virtual mappings beginning at PAGE_OFFSET.

I guess this doesn't matter on reboot or am I missing something else?

>
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>

Acked-by: Borislav Petkov <borislav.petkov@xxxxxxx>

> ---
>
> arch/x86/kernel/trampoline.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> --- 2.6.36-rc2/arch/x86/kernel/trampoline.c.0 2010-08-22 18:56:44.000000000 -0700
> +++ linux/arch/x86/kernel/trampoline.c 2010-08-24 22:11:08.000000000 -0700
> @@ -45,8 +45,7 @@ void __init setup_trampoline_page_table(
> /* Copy kernel address range */
> clone_pgd_range(trampoline_pg_dir + KERNEL_PGD_BOUNDARY,
> swapper_pg_dir + KERNEL_PGD_BOUNDARY,
> - min_t(unsigned long, KERNEL_PGD_PTRS,
> - KERNEL_PGD_BOUNDARY));
> + KERNEL_PGD_PTRS);
>
> /* Initialize low mappings */
> clone_pgd_range(trampoline_pg_dir,
>

--
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach
General Managers: Alberto Bozzo, Andrew Bowd
Registration: Dornach, Gemeinde Aschheim, Landkreis Muenchen
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