Re: [Xen-devel] [PATCH v2 03/16] Xen: xlate: Use page_to_xen_pfn instead of page_to_pfn

[Shannon Zhao <shannon.zhao@linaro.org>]

On 2016/1/19 22:59, Stefano Stabellini wrote:
> On Mon, 18 Jan 2016, Shannon Zhao wrote:
>> On 2016/1/16 1:08, Stefano Stabellini wrote:
>>> On Fri, 15 Jan 2016, Shannon Zhao wrote:
>>>> From: Shannon Zhao <shannon.zhao@linaro.org>
>>>>
>>>> Use page_to_xen_pfn in case of 64KB page.
>>>>
>>>> Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
>>>> ---
>>>>   drivers/xen/xlate_mmu.c | 2 +-
>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c
>>>> index 9692656..b9fcc2c 100644
>>>> --- a/drivers/xen/xlate_mmu.c
>>>> +++ b/drivers/xen/xlate_mmu.c
>>>> @@ -227,7 +227,7 @@ int __init xen_xlate_map_ballooned_pages(xen_pfn_t **gfns, void **virt,
>>>>   		return rc;
>>>>   	}
>>>>   	for (i = 0; i < nr_grant_frames; i++)
>>>> -		pfns[i] = page_to_pfn(pages[i]);
>>>> +		pfns[i] = page_to_xen_pfn(pages[i]);
>>>
>>> Shannon, thanks for the patch.
>>>
>>> Keeping in mind that in the 64K case, kernel pages are 64K but xen pages
>>> are still 4K, I think you also need to allocate
>>> (nr_grant_frames/XEN_PFN_PER_PAGE) kernel pages (assuming that they are
>>> allocated contiguously): nr_grant_frames refers to 4K pages, while
>>> xen_xlate_map_ballooned_pages is allocating pages on a 64K granularity
>>> (sizeof(pages[0]) == 64K).
>>>
>>> Be careful that alloc_xenballooned_pages deals with 64K pages (because
>>> it deals with kernel pages), while xen_pfn_t is always 4K based (because
>>> it deals with Xen pfns).
>>>
>>> Please test it with and without CONFIG_ARM64_64K_PAGES. Thanks!
>>>
>> Stefano, thanks for your explanation. How about below patch?
>
> Good work, it looks like you covered all bases, I think it should work,
> but I haven't tested it myself. Just one note below.
>
>
>> diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c
>> index 9692656..e1f7c95 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] = xen_pfn++;
>> +       }
>
> We might want to:
>
>    pfns[i] = pfn_to_gfn(xen_pfn++);
>
> for consistency, even though for autotranslate guests pfn_to_gfn always
> returns pfn.
>
Ok, will add. Thanks.

>
>> -       vaddr = vmap(pages, nr_grant_frames, 0, PAGE_KERNEL);
>> +       vaddr = vmap(pages, nr_pages, 0, PAGE_KERNEL);
>>          if (!vaddr) {
>> -               pr_warn("%s Couldn't map %ld pfns rc:%d\n", __func__,
>> -                       nr_grant_frames, rc);
>> -               free_xenballooned_pages(nr_grant_frames, pages);
>> +               pr_warn("%s Couldn't map %ld pages rc:%d\n", __func__,
>> +                       nr_pages, rc);
>> +               free_xenballooned_pages(nr_pages, pages);
>>                  kfree(pages);
>>                  kfree(pfns);
>>                  return -ENOMEM;
>>
>> --
>> Shannon
>>

-- 
Shannon