Re: [PATCH] x86: fix determination of bit count for struct domain allocations

[Andrew Cooper <andrew.cooper3@citrix.com>]

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On 14/03/14 15:23, Jan Beulich wrote:
> We can't just add in the hole shift value, as the hole may be at or
> above the 44-bit boundary. Instead we need to determine the total bit
> count until reaching 32 significant (not squashed out) bits in PFN
> representations.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>
> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -180,6 +180,19 @@ void dump_pageframe_info(struct domain *
>      spin_unlock(&d->page_alloc_lock);
>  }
>  
> +static unsigned int __init noinline _domain_struct_bits(void)

noinline for debugging purposes?

~Andrew

> +{
> +    unsigned int bits = 32 + PAGE_SHIFT;
> +    unsigned int sig = hweight32(~pfn_hole_mask);
> +    unsigned int mask = pfn_hole_mask >> 32;
> +
> +    for ( ; bits < BITS_PER_LONG && sig < 32; ++bits, mask >>= 1 )
> +        if ( !(mask & 1) )
> +            ++sig;
> +
> +    return bits;
> +}
> +
>  struct domain *alloc_domain_struct(void)
>  {
>      struct domain *d;
> @@ -187,7 +200,10 @@ struct domain *alloc_domain_struct(void)
>       * We pack the PDX of the domain structure into a 32-bit field within
>       * the page_info structure. Hence the MEMF_bits() restriction.
>       */
> -    unsigned int bits = 32 + PAGE_SHIFT + pfn_pdx_hole_shift;
> +    static unsigned int __read_mostly bits;
> +
> +    if ( unlikely(!bits) )
> +         bits = _domain_struct_bits();
>  
>      BUILD_BUG_ON(sizeof(*d) > PAGE_SIZE);
>      d = alloc_xenheap_pages(0, MEMF_bits(bits));
>
>
>
>
>
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> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel


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