Re: [PATCH v2 16/17] libxc/xc_dom_arm: Copy ACPI tables to guest space

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

Hi Shannon,

On 12/07/16 04:47, Shannon Zhao wrote:
> On 2016/7/6 18:12, Stefano Stabellini wrote:
>> On Wed, 6 Jul 2016, Julien Grall wrote:
>>>> On 05/07/16 18:13, Stefano Stabellini wrote:
>>>>>> On Thu, 23 Jun 2016, Julien Grall wrote:
>>>>>>>> On 23/06/2016 04:17, Shannon Zhao wrote:
>>>>>>>>>> From: Shannon Zhao <shannon.zhao@linaro.org>
>>>>>>>>>> +static int xc_dom_copy_acpi(struct xc_dom_image *dom)
>>>>>>>>>> +{
>>>>>>>>>> +    int rc, i;
>>>>>>>>>> +    uint32_t pages_num = ROUNDUP(dom->acpitable_size, XC_PAGE_SHIFT) >>
>>>>>>>>>> +                         XC_PAGE_SHIFT;
>>>>>>>>>> +    const xen_pfn_t base = GUEST_ACPI_BASE >> XC_PAGE_SHIFT;
>>>>>>>>>> +    xen_pfn_t *p2m;
>>>>>>>>>> +    void *acpi_pages;
>>>>>>>>>> +
>>>>>>>>>> +    p2m = malloc(pages_num * sizeof(*p2m));
>>>>>>>>>> +    for (i = 0; i < pages_num; i++)
>>>>>>>>>> +        p2m[i] = base + i;
>>>>>>>>>> +
>>>>>>>>>> +    rc = xc_domain_populate_physmap_exact(dom->xch, dom->guest_domid,
>>>>>>>>>> +                                          pages_num, 0, 0, p2m);
>>>>>>>>
>>>>>>>> Hmmmm... it looks like this is working because libxl is setting the
>>>>>>>> maximum
>>>>>>>> size of the domain with some slack (1MB). However, I guess the slack was
>>>>>>>> for
>>>>>>>> something else. Wei, Stefano, Ian, can you confirm?
>>>>>>
>>>>>> If I recall correctly, the slack is a magic value coming from the
>>>>>> ancient history of toolstacks.
>>>>
>>>> Does it mean we would need to update the slack to take into account the ACPI
>>>> blob?
>> Yes, we need to take into account the ACPI blob. Probably not in the
>> slack but directly in mam_memkb.
> Sorry, I'm not sure understand this. I found the b_info->max_memkb but
> didn't find the slack you said. And how to fix this? Update
> b_info->max_memkb or the slack?

You can give a look to LIBXL_MAXMEM_CONSTANT.

I am not very familiar with libxl, so I will let Wei and Stefano giving 
you advice on how to fix this.

Regards,

-- 
Julien Grall

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