Ping: [PATCH v2 6/9] x86/p2m: avoid unnecessary calls of write_p2m_entry_pre() hook

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.11.2020 10:37, Jan Beulich wrote:
> When shattering a large page, we first construct the new page table page
> and only then hook it up. The "pre" hook in this case does nothing, for
> the page starting out all blank. Avoid 512 calls into shadow code in
> this case by passing in INVALID_GFN, indicating the page being updated
> is (not yet) associated with any GFN. (The alternative to this change
> would be to actually pass in a correct GFN, which can't be all the same
> on every loop iteration.)
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v2: New.

Ping?

Thanks, Jan

> --- a/xen/arch/x86/mm/p2m-pt.c
> +++ b/xen/arch/x86/mm/p2m-pt.c
> @@ -134,7 +134,7 @@ static int write_p2m_entry(struct p2m_do
>  
>          paging_lock(d);
>  
> -        if ( p2m->write_p2m_entry_pre )
> +        if ( p2m->write_p2m_entry_pre && gfn != gfn_x(INVALID_GFN) )
>              p2m->write_p2m_entry_pre(d, gfn, p, new, level);
>  
>          oflags = l1e_get_flags(*p);
> @@ -290,7 +290,8 @@ p2m_next_level(struct p2m_domain *p2m, v
>          {
>              new_entry = l1e_from_pfn(pfn | (i << ((level - 1) * 
> PAGETABLE_ORDER)),
>                                       flags);
> -            rc = write_p2m_entry(p2m, gfn, l1_entry + i, new_entry, level);
> +            rc = write_p2m_entry(p2m, gfn_x(INVALID_GFN), l1_entry + i,
> +                                 new_entry, level);
>              if ( rc )
>              {
>                  unmap_domain_page(l1_entry);
> 
>