Re: [Xen-devel] [PATCH] xen/arm: p2m: Don't create new table when the mapping is removed

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 18 Dec 2013, Julien Grall wrote:
> When  Xen is removing/relinquishing mapping, it will create second/third 
> tables
> if they don't exist.
> 
> Non-existent table means the address range was never mapped, so Xen can safely
> skip them.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> 
> ---
>     Release: This is an improvement for Xen 4.4. It will save time during
>     relinquish phase and avoid dummy allocation.
>     The downside is the patch is modifying p2m loop which is used everywhere.
> ---
>  xen/arch/arm/p2m.c |   22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index d24a6fc..9ef8819 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -246,10 +246,12 @@ static int create_p2m_entries(struct domain *d,
>                    cur_first_offset = ~0,
>                    cur_second_offset = ~0;
>      unsigned long count = 0;
> +    bool_t populate = (op == INSERT || op == ALLOCATE);

why don't you just check for op == REMOVE?


>      spin_lock(&p2m->lock);
>  
> -    for(addr = start_gpaddr; addr < end_gpaddr; addr += PAGE_SIZE)
> +    addr = start_gpaddr;
> +    while ( addr < end_gpaddr )
>      {
>          if ( cur_first_page != p2m_first_level_index(addr) )
>          {
> @@ -265,8 +267,15 @@ static int create_p2m_entries(struct domain *d,
>  
>          if ( !first[first_table_offset(addr)].p2m.valid )
>          {
> +            if ( !populate )
> +            {
> +                addr += FIRST_SIZE;
> +                continue;
> +            }
> +
>              rc = p2m_create_table(d, &first[first_table_offset(addr)]);
> -            if ( rc < 0 ) {
> +            if ( rc < 0 )
> +            {
>                  printk("p2m_populate_ram: L1 failed\n");
>                  goto out;
>              }
> @@ -284,6 +293,12 @@ static int create_p2m_entries(struct domain *d,
>  
>          if ( !second[second_table_offset(addr)].p2m.valid )
>          {
> +            if ( !populate )
> +            {
> +                addr += SECOND_SIZE;
> +                continue;
> +            }
> +
>              rc = p2m_create_table(d, &second[second_table_offset(addr)]);
>              if ( rc < 0 ) {
>                  printk("p2m_populate_ram: L2 failed\n");
> @@ -372,6 +387,9 @@ static int create_p2m_entries(struct domain *d,
>              }
>              count = 0;
>          }
> +
> +        /* Got the next page */
> +        addr += PAGE_SIZE;
>      }
>  
>      if ( op == ALLOCATE || op == INSERT )
> -- 
> 1.7.10.4
> 

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