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

[Borislav Petkov <borislav.petkov@amd.com>]

From: Hugh Dickins <hughd@google.com>
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@google.com>

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

> ---
> 
>  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.

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