Re: [PATCH] [RFC] xen: Fix memory hotplug end limit test for updating compat M2P table

["Jan Beulich" <JBeulich@suse.com>]

>>> On 23.04.12 at 20:07, Malcolm Crossley <malcolm.crossley@citrix.com> wrote:
> The memory hotplug code was masking the hotplugged memory start address and 
> comparing to a shifted version of COMPAT MPT size but not doing the same for 
> the end address.
> This patch applies the same shifting and masking to the end address and 
> reapplies the mask if the end address has been clamped.

This lacks a Signed-off-by tag in any case.

I'm not, however, seeing what is being fixed here:
RDWR_COMPAT_MPT_VIRT_{START,END} are both aligned to a
1Gb boundary, so I'm not immediately seeing how the adjustment
would result in any changed behavior.

Also, assuming I'm overlooking something and the patch is indeed
needed (and hence you'll resubmit), please fix the indentation to
not use hard tabs, and adjust the lines you change anyway to
match Xen's coding style.

Jan

> diff -r 274e5accd62d -r 8470671d407f xen/arch/x86/x86_64/mm.c
> --- a/xen/arch/x86/x86_64/mm.c
> +++ b/xen/arch/x86/x86_64/mm.c
> @@ -446,6 +446,8 @@ static int setup_compat_m2p_table(struct
>      int err = 0;
>  
>      smap = info->spfn & (~((1UL << (L2_PAGETABLE_SHIFT - 2)) -1));
> +    emap = ( (epfn + ((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1 )) &
> +                ~((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1) );
>  
>      /*
>       * Notice: For hot-added memory, only range below m2p_compat_vstart
> @@ -454,11 +456,11 @@ static int setup_compat_m2p_table(struct
>      if   ((smap > ((RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START) >> 
> 2)) )
>          return 0;
>  
> -    if (epfn > (RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START))
> -        epfn = (RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START) >> 2;
> -
> -    emap = ( (epfn + ((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1 )) &
> -                ~((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1) );
> +    if (emap > ((RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START) >> 2))
> +    {
> +        emap = (RDWR_COMPAT_MPT_VIRT_END - RDWR_COMPAT_MPT_VIRT_START) >> 2;
> +    	emap = emap & ~((1UL << (L2_PAGETABLE_SHIFT - 2)) - 1);
> +    }
>  
>      va = HIRO_COMPAT_MPT_VIRT_START +
>           smap * sizeof(*compat_machine_to_phys_mapping);
> 
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