Re: [Xen-devel] [PATCH v7 03/17] Xen: xlate: Use page_to_xen_pfn instead of page_to_pfn

[Julien Grall <julien.grall@xxxxxxx>]

Hi Shannon,

On 24/03/16 14:44, Shannon Zhao wrote:
> Make xen_xlate_map_ballooned_pages work with 64K pages. In that case
> Kernel pages are 64K in size but Xen pages remain 4K in size. Xen pfns
> refer to 4K pages.
>
> Signed-off-by: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
> Reviewed-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> ---
>   drivers/xen/xlate_mmu.c | 26 ++++++++++++++++----------
>   1 file changed, 16 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c
> index 9692656..28f728b 100644
> --- a/drivers/xen/xlate_mmu.c
> +++ b/drivers/xen/xlate_mmu.c
> @@ -207,9 +207,12 @@ int __init xen_xlate_map_ballooned_pages(xen_pfn_t **gfns, 
> void **virt,
>         void *vaddr;
>         int rc;
>         unsigned int i;
> +       unsigned long nr_pages;
> +       xen_pfn_t xen_pfn = 0;
>
>         BUG_ON(nr_grant_frames == 0);
> -       pages = kcalloc(nr_grant_frames, sizeof(pages[0]), GFP_KERNEL);
> +       nr_pages = DIV_ROUND_UP(nr_grant_frames, XEN_PFN_PER_PAGE);
> +       pages = kcalloc(nr_pages, sizeof(pages[0]), GFP_KERNEL);
>         if (!pages)
>                 return -ENOMEM;
>
> @@ -218,22 +221,25 @@ int __init xen_xlate_map_ballooned_pages(xen_pfn_t 
> **gfns, void **virt,
>                 kfree(pages);
>                 return -ENOMEM;
>         }
> -       rc = alloc_xenballooned_pages(nr_grant_frames, pages);
> +       rc = alloc_xenballooned_pages(nr_pages, pages);
>         if (rc) {
> -               pr_warn("%s Couldn't balloon alloc %ld pfns rc:%d\n", __func__,
> -                       nr_grant_frames, rc);
> +               pr_warn("%s Couldn't balloon alloc %ld pages rc:%d\n", __func__,
> +                       nr_pages, rc);
>                 kfree(pages);
>                 kfree(pfns);
>                 return rc;
>         }
> -       for (i = 0; i < nr_grant_frames; i++)
> -               pfns[i] = page_to_pfn(pages[i]);
> +       for (i = 0; i < nr_grant_frames; i++) {
> +               if ((i % XEN_PFN_PER_PAGE) == 0)
> +                       xen_pfn = page_to_xen_pfn(pages[i / XEN_PFN_PER_PAGE]);
> +               pfns[i] = pfn_to_gfn(xen_pfn++);
> +       }
Would it be possible to re-use xen_for_each_gfn? This will avoid 
open-coding the loop to break down the Linux page.
Regards,

--
Julien Grall

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