Re: [Xen-devel] [PATCH v1 20/20] libxl/acpi: Build ACPI tables for HVMlite guests

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 07/06/2016 12:04 PM, Julien Grall wrote:
> Hi Boris,
>
> On 06/07/16 16:50, Boris Ostrovsky wrote:
>> On 07/06/2016 07:05 AM, Julien Grall wrote:
>>>> +static int populate_acpi_pages(struct xc_dom_image *dom,
>>>> +                               xen_pfn_t *extents,
>>>> +                               unsigned int num_pages,
>>>> +                               struct acpi_ctxt *ctxt)
>>>> +{
>>>> +    int rc;
>>>> +    xc_interface *xch = dom->xch;
>>>> +    uint32_t domid = dom->guest_domid;
>>>> +    unsigned long idx, first_high_idx = (1ull << (32 -
>>>> ctxt->page_shift));
>>>> +
>>>> +    for (; num_pages; num_pages--, extents++) {
>>>> +
>>>> +        if (xc_domain_populate_physmap(xch, domid, 1, 0, 0, extents)
>>>> == 1)
>>>
>>> It looks like this is working because libxl is setting the maximum
>>> size of the domain with some slack (1MB). You might get in trouble if
>>> the slack is reduced or used by someone or the ACPI blob is increasing.
>>
>>
>> I saw your conversation about slack with Stefano and I am not sure I
>> understood what it was about. If this was about padding guest's memory
>> to be able to put there some additional data (such ACPI tables) then
>> this is not my intention here: if I can't populate (because it is
>> already populated, I guess) then I try to move memory around with code
>> below. That's what mem_hole_populate_ram() does as well.
>
> The maximum amount of memory that could be assigned to a domain is
> fixed per-domain. This maximum amount does not take into account the
> size of the ACPI blob. So you may end up to fail because all the
> memory was assigned somewhere else.

Why shouldn't max amount of guest's memory include ACPI tables? I think
we should fail and not rely on this slack if no more memory is available.

...

>
>>
>>> However, as mentioned in the ACPI thread [1], all the blobs are
>>> generally loaded by libxc and not libxl. This is more true on ARM
>>> because the guest address space is controlled by libxc (the position
>>> of all the blob are decided by it).
>>
>> The difference is that I not only load the tables here but also build
>> them. Which may or may not be the right thing to do in libxc.
>>
>> I suppose I can defer loading (and then keep pointer to tables in
>> acpitable_blob) but the then I need to keep RSDP descriptor somewhere
>> else (it is not part of the blob since it lives in lower MB of the
>> guest).
>
> The device tree for ARM are built in libxl and loaded for libxc. IHMO,
> it would be strange to have a different pattern for ACPI. 

Is RSDP part of the ACPI blob for ARM? If not, how do you load it?

-boris


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