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

Julien Grall
2016-03-30T11:22:56Z

Hi Shannon,

On 30/03/16 08:38, Shannon Zhao wrote:
>
>
> On 2016/3/30 0:28, Julien Grall wrote:
>> 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@linaro.org>
>>> Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
>>> ---
>>> 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.
> I don't think so. Using xen_acpi_guest_init will require factoring
> "pfns[i] = pfn_to_gfn(xen_pfn++)" to a function with parameter pfns[i].
> How can we pass pfns[i]?

By using the variable data. Something along those lines:

struct map_balloon_pages
{
xen_pfn_t *pfns;
unsigned int idx;
};

static void setup_balloon_gfn(unsigned long gfn, void *data)
{
struct map_balloon_pages *info = data;

data->pfns[data->idx] = gfn;
data->idx++;
}

And then in xen_xlate_map_ballooned_pages

xen_for_each_gfn(pages, nr_grant_frames, setup_balloon_gfn, &data);

Regards,

--
Julien Grall