Max gpfn for PV guests

Max gpfn for PV guests

[Aravindh Puthiyaparambil (aravindp)]

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I am trying to find out the max pgfn for a 256MB PV guest. If I call xc_domain_getinfolist() and look at xc_domaininfo->max_pages, I get 0x10100. If I call xc_domain_getinfo() and look at xc_dominfo->nr_pages, I get 0x10000. Within the hypervisor if I call domain_get_maximum_gpfn(), I get 0xffff. So it looks like xc_domain_getinfo() is returning the correct value. Why is xc_domain_getinfolist() returning a different value? Which value should I be looking at for the max gpfn?

Thanks,
Aravindh


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Re: Max gpfn for PV guests

[Jan Beulich]

>>> On 08.11.13 at 21:58, "Aravindh Puthiyaparambil (aravindp)"
<aravindp@cisco.com> wrote:
> I am trying to find out the max pgfn for a 256MB PV guest. If I call 
> xc_domain_getinfolist() and look at xc_domaininfo->max_pages, I get 0x10100. If 
> I call xc_domain_getinfo() and look at xc_dominfo->nr_pages, I get 0x10000. 
> Within the hypervisor if I call domain_get_maximum_gpfn(), I get 0xffff. So 
> it looks like xc_domain_getinfo() is returning the correct value. Why is 
> xc_domain_getinfolist() returning a different value? Which value should I be 
> looking at for the max gpfn?

I'm afraid none of these - since PV guests control the P2M mapping
themselves, there simply is no "max GPFN" being tracked here. (The
value returned by domain_get_maximum_gpfn() originates from the
shared info structure, i.e. again is only valid if the guest cares to
maintain that field.)

Jan

Re: Max gpfn for PV guests

[Aravindh Puthiyaparambil (aravindp)]

>>>> On 08.11.13 at 21:58, "Aravindh Puthiyaparambil (aravindp)"
><aravindp@cisco.com> wrote:
>> I am trying to find out the max pgfn for a 256MB PV guest. If I call
>> xc_domain_getinfolist() and look at xc_domaininfo->max_pages, I get
>> 0x10100. If I call xc_domain_getinfo() and look at xc_dominfo->nr_pages, I
>get 0x10000.
>> Within the hypervisor if I call domain_get_maximum_gpfn(), I get
>> 0xffff. So it looks like xc_domain_getinfo() is returning the correct
>> value. Why is
>> xc_domain_getinfolist() returning a different value? Which value
>> should I be looking at for the max gpfn?
>
>I'm afraid none of these - since PV guests control the P2M mapping
>themselves, there simply is no "max GPFN" being tracked here. (The value
>returned by domain_get_maximum_gpfn() originates from the shared info
>structure, i.e. again is only valid if the guest cares to maintain that field.)

Does this also hold true for PV guests running with shadow page tables?

Thanks,
Aravindh

Re: Max gpfn for PV guests

[Jan Beulich]

>>> On 11.11.13 at 17:42, "Aravindh Puthiyaparambil (aravindp)"
<aravindp@cisco.com> wrote:
>>>>> On 08.11.13 at 21:58, "Aravindh Puthiyaparambil (aravindp)"
>><aravindp@cisco.com> wrote:
>>> I am trying to find out the max pgfn for a 256MB PV guest. If I call
>>> xc_domain_getinfolist() and look at xc_domaininfo->max_pages, I get
>>> 0x10100. If I call xc_domain_getinfo() and look at xc_dominfo->nr_pages, I
>>get 0x10000.
>>> Within the hypervisor if I call domain_get_maximum_gpfn(), I get
>>> 0xffff. So it looks like xc_domain_getinfo() is returning the correct
>>> value. Why is
>>> xc_domain_getinfolist() returning a different value? Which value
>>> should I be looking at for the max gpfn?
>>
>>I'm afraid none of these - since PV guests control the P2M mapping
>>themselves, there simply is no "max GPFN" being tracked here. (The value
>>returned by domain_get_maximum_gpfn() originates from the shared info
>>structure, i.e. again is only valid if the guest cares to maintain that 
> field.)
> 
> Does this also hold true for PV guests running with shadow page tables?

I would think so, but I don't know enough about this mode to be
certain.

Jan

Re: Max gpfn for PV guests

[Tim Deegan]

At 16:47 +0000 on 11 Nov (1384184876), Jan Beulich wrote:
> >>> On 11.11.13 at 17:42, "Aravindh Puthiyaparambil (aravindp)"
> <aravindp@cisco.com> wrote:
> >>>>> On 08.11.13 at 21:58, "Aravindh Puthiyaparambil (aravindp)"
> >><aravindp@cisco.com> wrote:
> >>> I am trying to find out the max pgfn for a 256MB PV guest. If I call
> >>> xc_domain_getinfolist() and look at xc_domaininfo->max_pages, I get
> >>> 0x10100. If I call xc_domain_getinfo() and look at xc_dominfo->nr_pages, I
> >>get 0x10000.
> >>> Within the hypervisor if I call domain_get_maximum_gpfn(), I get
> >>> 0xffff. So it looks like xc_domain_getinfo() is returning the correct
> >>> value. Why is
> >>> xc_domain_getinfolist() returning a different value? Which value
> >>> should I be looking at for the max gpfn?
> >>
> >>I'm afraid none of these - since PV guests control the P2M mapping
> >>themselves, there simply is no "max GPFN" being tracked here. (The value
> >>returned by domain_get_maximum_gpfn() originates from the shared info
> >>structure, i.e. again is only valid if the guest cares to maintain that 
> > field.)
> > 
> > Does this also hold true for PV guests running with shadow page tables?
> 
> I would think so, but I don't know enough about this mode to be
> certain.

Yes; PV guests under shadow pagetables still control their own memory
layout.

Tim.