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

[Julien Grall <julien.grall@linaro.org>]

On 11/20/2013 01:13 PM, Ian Campbell wrote:
> On Wed, 2013-11-20 at 13:04 +0000, Julien Grall wrote:
>>
>> 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.
>
> That would be concern except the sizes are defined immediately above as
> shifts based on page numbers.
>
>>
>>> 8>------------------
>>>
>>>   From 079a2815d86567de1cbb541541d08a0b9ac3d18d Mon Sep 17 00:00:00 2001
>>> From: Ian Campbell <ian.campbell@citrix.com>
>>> 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@linaro.org>
>>> Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
>>> ---
>>>    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.
>
> That's not how ROUNDUP is defined in libxc:
> #define ROUNDUP(_x,_w) (((unsigned long)(_x)+(1UL<<(_w))-1) & ~((1UL<<(_w))-1))
>
> so it expects _w (width?) to be the shift.

Oh right, I though it was defined as in xen. In any case, I think you 
should use XC_DOM_PAGE_SHIFT(dom).

-- 
Julien Grall