Re: [Xen-devel] [PATCH for-4.6] x86/gdt: Drop write-only, xalloc()'d array from set_gdt()

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Aug 03, 2015 at 06:05:43PM +0100, Andrew Cooper wrote:
> It is not used, and can cause a spurious failure of the set_gdt() hypercall in
> low memory situations.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> ---

This array does appear to be write-only and never gets read.

FWIW

Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>

It's obviously correct and fixes a problem, so it can be applied to 4.6
tree.

>  xen/arch/x86/mm.c |    9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
> index 63aa666..4b76587 100644
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -4439,20 +4439,15 @@ long set_gdt(struct vcpu *v,
>      l1_pgentry_t *pl1e;
>      /* NB. There are 512 8-byte entries per GDT page. */
>      int i, nr_pages = (entries + 511) / 512;
> -    unsigned long *pfns;
>  
>      if ( entries > FIRST_RESERVED_GDT_ENTRY )
>          return -EINVAL;
>  
> -    pfns = xmalloc_array(unsigned long, nr_pages);
> -    if ( !pfns )
> -        return -ENOMEM;
> -
>      /* Check the pages in the new GDT. */
>      for ( i = 0; i < nr_pages; i++ )
>      {
>          struct page_info *page;
> -        pfns[i] = frames[i];
> +
>          page = get_page_from_gfn(d, frames[i], NULL, P2M_ALLOC);
>          if ( !page )
>              goto fail;
> @@ -4476,7 +4471,6 @@ long set_gdt(struct vcpu *v,
>          l1e_write(&pl1e[i], l1e_from_pfn(frames[i], __PAGE_HYPERVISOR_RW));
>      }
>  
> -    xfree(pfns);
>      return 0;
>  
>   fail:
> @@ -4484,7 +4478,6 @@ long set_gdt(struct vcpu *v,
>      {
>          put_page_and_type(mfn_to_page(frames[i]));
>      }
> -    xfree(pfns);
>      return -EINVAL;
>  }
>  
> -- 
> 1.7.10.4

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