Re: [Xen-devel] [PATCH v2 15/16] xen/arm: mm: Introduce temporary variable in create_xen_entries

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 19 Jun 2017, Julien Grall wrote:
> This is improving the code readability and avoid to dereference the
> table every single time we need to access the entry.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> 
>     Changes in v2:
>         - Patch added
> ---
>  xen/arch/arm/mm.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 6241c53821..657fee0b17 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -986,28 +986,30 @@ static int create_xen_entries(enum xenmap_operation op,
>  {
>      int rc;
>      unsigned long addr = virt, addr_end = addr + nr_mfns * PAGE_SIZE;
> -    lpae_t pte;
> +    lpae_t pte, *entry;
>      lpae_t *third = NULL;
>  
>      for(; addr < addr_end; addr += PAGE_SIZE, mfn = mfn_add(mfn, 1))
>      {
> -        if ( !lpae_table(xen_second[second_linear_offset(addr)]) )
> +        entry = &xen_second[second_linear_offset(addr)];
> +        if ( !lpae_table(*entry) )
>          {
> -            rc = create_xen_table(&xen_second[second_linear_offset(addr)]);
> +            rc = create_xen_table(entry);
>              if ( rc < 0 ) {
>                  printk("create_xen_entries: L2 failed\n");
>                  goto out;
>              }
>          }
>  
> -        BUG_ON(!lpae_valid(xen_second[second_linear_offset(addr)]));
> +        BUG_ON(!lpae_valid(*entry));
>  
> -        third = mfn_to_virt(xen_second[second_linear_offset(addr)].pt.base);
> +        third = mfn_to_virt(entry->pt.base);
> +        entry = &third[third_table_offset(addr)];
>  
>          switch ( op ) {
>              case INSERT:
>              case RESERVE:
> -                if ( lpae_valid(third[third_table_offset(addr)]) )
> +                if ( lpae_valid(*entry) )
>                  {
>                      printk("create_xen_entries: trying to replace an 
> existing mapping addr=%lx mfn=%"PRI_mfn"\n",
>                             addr, mfn_x(mfn));
> @@ -1017,11 +1019,11 @@ static int create_xen_entries(enum xenmap_operation 
> op,
>                      break;
>                  pte = mfn_to_xen_entry(mfn, ai);
>                  pte.pt.table = 1;
> -                write_pte(&third[third_table_offset(addr)], pte);
> +                write_pte(entry, pte);
>                  break;
>              case MODIFY:
>              case REMOVE:
> -                if ( !lpae_valid(third[third_table_offset(addr)]) )
> +                if ( !lpae_valid(*entry) )
>                  {
>                      printk("create_xen_entries: trying to %s a non-existing 
> mapping addr=%lx\n",
>                             op == REMOVE ? "remove" : "modify", addr);
> @@ -1031,7 +1033,7 @@ static int create_xen_entries(enum xenmap_operation op,
>                      pte.bits = 0;
>                  else
>                  {
> -                    pte = third[third_table_offset(addr)];
> +                    pte = *entry;
>                      pte.pt.ro = PTE_RO_MASK(ai);
>                      pte.pt.xn = PTE_NX_MASK(ai);
>                      if ( !pte.pt.ro && !pte.pt.xn )
> @@ -1041,7 +1043,7 @@ static int create_xen_entries(enum xenmap_operation op,
>                          return -EINVAL;
>                      }
>                  }
> -                write_pte(&third[third_table_offset(addr)], pte);
> +                write_pte(entry, pte);
>                  break;
>              default:
>                  BUG();
> -- 
> 2.11.0
> 

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