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 01:30 PM, Ian Campbell wrote:
> On Wed, 2013-11-20 at 13:17 +0000, Julien Grall wrote:
>>
>> 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@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.
>>>
>>> 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).
> 
> Those macros are almost unused in libxc. I suspect they are leftovers
> from ia64 support, that being the only platform which we've supported
> which had the possibility of non-4k pages.

Sorry, I have only checked xc_dom_core.c

For your patch:

Acked-by: Julien Grall <julien.grall@xxxxxxxxxx>

-- 
Julien Grall

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