Re: [Xen-devel] [PATCH v3 1/3] xen/arm: implement steal_page

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Aug 05, 2013 at 05:40:54PM +0100, Stefano Stabellini wrote:
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> ---
>  xen/arch/arm/mm.c |   43 +++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 43 insertions(+), 0 deletions(-)
> 
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index f301e65..ea64c03 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -751,6 +751,49 @@ int donate_page(struct domain *d, struct page_info 
> *page, unsigned int memflags)
>  int steal_page(
>      struct domain *d, struct page_info *page, unsigned int memflags)
>  {
> +    unsigned long x, y;
> +    bool_t drop_dom_ref = 0;

Shouldn't this be true or false?

> +
> +    spin_lock(&d->page_alloc_lock);
> +
> +    if ( is_xen_heap_page(page) || (page_get_owner(page) != d) )
> +        goto fail;
> +
> +    /*
> +     * We require there is just one reference (PGC_allocated). We temporarily
> +     * drop this reference now so that we can safely swizzle the owner.
> +     */
> +    y = page->count_info;
> +    do {
> +        x = y;
> +        if ( (x & (PGC_count_mask|PGC_allocated)) != (1 | PGC_allocated) )
> +            goto fail;
> +        y = cmpxchg(&page->count_info, x, x & ~PGC_count_mask);
> +    } while ( y != x );
> +
> +    /* Swizzle the owner then reinstate the PGC_allocated reference. */
> +    page_set_owner(page, NULL);
> +    y = page->count_info;
> +    do {
> +        x = y;
> +        BUG_ON((x & (PGC_count_mask|PGC_allocated)) != PGC_allocated);
> +    } while ( (y = cmpxchg(&page->count_info, x, x | 1)) != x );
> +
> +    /* Unlink from original owner. */
> +    if ( !(memflags & MEMF_no_refcount) && !domain_adjust_tot_pages(d, -1) )
> +        drop_dom_ref = 1;
> +    page_list_del(page, &d->page_list);
> +
> +    spin_unlock(&d->page_alloc_lock);
> +    if ( unlikely(drop_dom_ref) )
> +        put_domain(d);
> +    return 0;
> +
> + fail:
> +    spin_unlock(&d->page_alloc_lock);
> +    printk("Bad page %p: ed=%p(%u), sd=%p, caf=%08lx, taf=%lx\n",
> +            (void *)page_to_mfn(page), d, d->domain_id,
> +            page_get_owner(page), page->count_info, page->u.inuse.type_info);
>      return -1;
>  }
>  
> -- 
> 1.7.2.5
> 
> 
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