Re: [PATCH] xen/arm: setup: initialize xenheap mappings after boot pages avaiable

[Julien Grall <julien.grall@arm.com>]

Hi Peng,

On 31/05/16 10:58, Peng Fan wrote:
>>
>>> So, need to make sure boot pages are ready before setup xenheap mappings.
>>
>> init_boot_pages is using mfn_to_virt (see bootmem_region_add), which cannot
>> work until xenheap_mfn_start is initialized. This is done by
>> setup_xenheap_mappings.
>
> My bad. I did not catch this point. Thanks for correcting me.
>
>>
>> I would be happy to give you hint on how to solve this, but I am not sure to
>> fully understand your issue. Can you give more details?
>
> I did not met issue on my platform. I just think the logic of this piece code
> may cause errors on platform with large memory (>512GB).
>
> How about the following patch?
> First loop all the memory banks and calculate ram_size/ram_start/ram_end,
> then set xenheap_virt_end/start and xenheap_mfn_end.
> Now readly for init boot pages and setup_xenheap_mappings.

Have you tested this patch? I would be surprised to see it working.

>
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index dcb23b7..d3a3af3 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -635,13 +635,24 @@ static void __init setup_mm(unsigned long dtb_paddr, size_t dtb_size)
>           paddr_t bank_start = bootinfo.mem.bank[bank].start;
>           paddr_t bank_size = bootinfo.mem.bank[bank].size;
>           paddr_t bank_end = bank_start + bank_size;
> -        paddr_t s, e;
>
>           ram_size = ram_size + bank_size;
>           ram_start = min(ram_start,bank_start);
>           ram_end = max(ram_end,bank_end);
> +    }
>
> -        setup_xenheap_mappings(bank_start>>PAGE_SHIFT, bank_size>>PAGE_SHIFT);
> +    total_pages += ram_size >> PAGE_SHIFT;
> +
> +    xenheap_virt_end = XENHEAP_VIRT_START + ram_end - ram_start;

XENHEAP_VIRT_START will be replaced by xenheap_virt_start which is not 
initialized at this time. It is done by setup_xenheap_mappings.

In any case, even if the variable are correctly setup the underlying 
page table are not present.

The easiest way I can think to fix the problem is splitting the bank 
with chunk of 512GB and calling setup_xenheap_mappings, init_boot_pages 
for each chunk.

It is not the nicest way, so I will happy if you find a better one.

Regards,

-- 
Julien Grall

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