Re: [Xen-devel] [PATCH v2] x86: debugging code for testing 16Tb support on smaller memory systems

[Tim Deegan <tim@xxxxxxx>]

At 14:26 +0000 on 23 Jan (1358951188), Jan Beulich wrote:
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -82,6 +82,11 @@ boolean_param("noapic", skip_ioapic_setu
>  s8 __read_mostly xen_cpuidle = -1;
>  boolean_param("cpuidle", xen_cpuidle);
>  
> +#ifndef NDEBUG
> +unsigned long __initdata highmem_start;
> +size_param("highmem-start", highmem_start);
> +#endif
> +
>  cpumask_t __read_mostly cpu_present_map;
>  
>  unsigned long __read_mostly xen_phys_start;
> @@ -787,6 +792,14 @@ void __init __start_xen(unsigned long mb
>      modules_headroom = bzimage_headroom(bootstrap_map(mod), mod->mod_end);
>      bootstrap_map(NULL);
>  
> +#ifndef highmem_start
> +    /* Don't allow split below 4Gb. */
> +    if ( highmem_start < GB(4) )
> +        highmem_start = 0;
> +    else /* align to L3 entry boundary */
> +        highmem_start &= ~((1UL << L3_PAGETABLE_SHIFT) - 1);
> +#endif

DYM #ifndef NDEBUG ?  I can see that checking for highmem_start being a
macro is strictly correct but it seems more vulnerable to later changes,
esp. since this:

> --- a/xen/include/asm-x86/setup.h
> +++ b/xen/include/asm-x86/setup.h
> @@ -43,4 +43,10 @@ void microcode_grab_module(
>  
>  extern uint8_t kbd_shift_flags;
>  
> +#ifdef NDEBUG
> +# define highmem_start 0
> +#else
> +extern unsigned long highmem_start;
> +#endif

happens so far away. 

Tim.

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