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

Shannon Zhao
2016-03-30T12:42:33Z

On 2016年03月30日 19:22, Julien Grall wrote:
> 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);
I think this looks like less direct. Anyway I will update this patch as
you said.

Thanks,
--
Shannon