Re: [Xen-devel] [PATCH] libxc/arm: align to page size the base address of the device tree

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 11/20/2013 09:48 AM, Ian Campbell wrote:
> On Tue, 2013-11-19 at 18:52 +0000, Julien Grall wrote:
> > xc_dom_alloc_segment requires start address to be page align.
> I wonder why I didn't see this? It seems very unlikely that my dtb would
> be exactly page sized, yet it works... Ah, I have >128M of RAM in my
> guest so the base would be 128M. Well spotted.
>
> I think it would be slightly preferable to round dtbsize up to a page.
> e.g. the following. What do you think?
Sounds good to me. I wrote my patch in the other way because I though 
RAM size can be non-page aligned.
> 8>------------------
>
>  From 079a2815d86567de1cbb541541d08a0b9ac3d18d Mon Sep 17 00:00:00 2001
> From: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Date: Wed, 20 Nov 2013 09:45:32 +0000
> Subject: [PATCH] libxl: arm: ensure DTB is page aligned
>
> xc_dom_alloc_segment requires this. Since rambase and ramend are both page
> aligned, rounding up the DTB is sufficient.
>
> Reported-by: Julien Grall <julien.grall@xxxxxxxxxx>
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> ---
>   tools/libxc/xc_dom_arm.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/libxc/xc_dom_arm.c b/tools/libxc/xc_dom_arm.c
> index ffe575b..a40e04d 100644
> --- a/tools/libxc/xc_dom_arm.c
> +++ b/tools/libxc/xc_dom_arm.c
> @@ -282,7 +282,7 @@ int arch_setup_meminit(struct xc_dom_image *dom)
>       {
>           const uint64_t rambase = dom->rambase_pfn << XC_PAGE_SHIFT;
>           const uint64_t ramend = rambase + ( dom->total_pages << XC_PAGE_SHIFT 
> );
> -        const uint64_t dtbsize = ( dom->devicetree_size + 3 ) & ~0x3;
> +        const uint64_t dtbsize = ROUNDUP(dom->devicetree_size, XC_PAGE_SHIFT);
XC_PAGE_SHIFT only contains the shift. You should use XC_PAGE_SIZE.

Even better, XC_DOM_PAGE_SIZE(dom), so we don't hardcode the size.

--
Julien Grall

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