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

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Date:	Fri, 15 Jan 2016 17:08:46 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Shannon Zhao <zhaoshenglong@...wei.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 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!



>  	vaddr = vmap(pages, nr_grant_frames, 0, PAGE_KERNEL);
>  	if (!vaddr) {
> -- 
> 2.0.4
> 
> 
> 
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>