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

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Message-ID: <569C7363.80106@huawei.com>
Date:	Mon, 18 Jan 2016 13:08:51 +0800
From:	Shannon Zhao <zhaoshenglong@...wei.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<ard.biesheuvel@...aro.org>, <stefano.stabellini@...rix.com>,
	<david.vrabel@...rix.com>, <mark.rutland@....com>,
	<devicetree@...r.kernel.org>, <linux-efi@...r.kernel.org>,
	<catalin.marinas@....com>, <will.deacon@....com>,
	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xen.org>,
	<julien.grall@...rix.com>, <shannon.zhao@...aro.org>,
	<peter.huangpeng@...wei.com>
Subject: Re: [Xen-devel] [PATCH v2 03/16] Xen: xlate: Use page_to_xen_pfn
 instead of page_to_pfn



On 2016/1/16 1:08, Stefano Stabellini wrote:
> On Fri, 15 Jan 2016, Shannon Zhao wrote:
>> From: Shannon Zhao <shannon.zhao@...aro.org>
>>
>> Use page_to_xen_pfn in case of 64KB page.
>>
>> Signed-off-by: Shannon Zhao <shannon.zhao@...aro.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?

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++;
+       }

-       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