Re: [Xen-devel] [PATCH v3] xen/arm: Fix crash if last memory section is bigger than 1gb

[Frediano Ziglio <freddy77@xxxxxxxxx>]

2014-10-03 10:09 GMT+01:00 Ian Campbell <Ian.Campbell@xxxxxxxxxx>:
> On Thu, 2014-10-02 at 16:16 +0100, Frediano Ziglio wrote:
>> setup_xenheap_mappings setup head memory on Arm 32 has a limit of 1gb.
>> On system with large memory is possible that there are no blocks of memory
>> smaller than 1gb leading xenheap_pages to be more than 1gb.
>> This cause memory errors trying to access heap after the 1gb limit.
>
> As I mentioned in a previous round of review this explanation doesn't
> really fit.
>
> I think better would be:
>
>         On arm32 the xenheap has a maximum size of 1GB. On systems with
>         more than 8GB (so 1/8 total RAM is greater than 1GB) there is no
>         point in searching for a region with 1/8 of the total RAM when
>         only 1GB will be used. Therefore limit the maximum size to 1GB
>         before searching.
>
> If you agree I will make this change upon commit.
>

Agree. This explains the real reason of the change.

Frediano

>>
>> Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
>> Reviewed-by: Julien Grall <julien.grall@xxxxxxxxxx>
>> ---
>>  xen/arch/arm/setup.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
>> index 446de8a..c43c776 100644
>> --- a/xen/arch/arm/setup.c
>> +++ b/xen/arch/arm/setup.c
>> @@ -500,7 +500,7 @@ static void __init setup_mm(unsigned long
>> dtb_paddr, size_t dtb_size)
>>       *
>>       *  - must be 32 MiB aligned
>>       *  - must not include Xen itself or the boot modules
>> -     *  - must be at most 1/8 the total RAM in the system
>> +     *  - must be at most 1GB or 1/8 the total RAM in the system if less
>>       *  - must be at least 128M
>>       *
>>       * We try to allocate the largest xenheap possible within these
>> @@ -509,6 +509,7 @@ static void __init setup_mm(unsigned long
>> dtb_paddr, size_t dtb_size)
>>      heap_pages = ram_pages;
>>      xenheap_pages = (heap_pages/8 + 0x1fffUL) & ~0x1fffUL;
>>      xenheap_pages = max(xenheap_pages, 128UL<<(20-PAGE_SHIFT));
>> +    xenheap_pages = min(xenheap_pages, 1UL<<(30-PAGE_SHIFT));
>>
>>      do
>>      {
>
>

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