Subject: [PATCH 4/8] xen: Use the correctly the Xen memory terminologies

From: [email-masked] (Boris Ostrovsky)
Date: Wed, 29 Jul 2015 10:51:18 -0400

On 07/29/2015 10:23 AM, Julien Grall wrote:
> On 29/07/15 15:14, Boris Ostrovsky wrote:
>>> static inline unsigned long pfn_to_gfn(unsigned long pfn)
>>> {
>>>      if (xen_feature(XENFEAT_autotranslated_physmap))
>>>          return pfn;
>>>      else
>>>          return pfn_to_mfn(pfn);
>>> }
>>
>> But you'd still say 'op.arg1.mfn = pfn_to_gfn(pfn);' in xen_do_pin()
>> i.e. assign GFN to MFN, right? That's what I was referring to.
> Well no. I would use op.arg1.mfn = pfn_to_mfn(pfn) given that the code,
> if I'm right, is only executed for PV.
>
> mfn = pfn_to_gfn(...) was valid too because on PV is always an MFN. The
> suggestion of pfn_to_mfn was just for more readability,

Right, and my comments were also not about correctness.

>
>> (In general, I am not sure a guest should ever use 'mfn' as it is purely
>> a hypervisor construct. Including p2m, which I think should really be
>> p2g as this is what we use to figure out what to stick into page tables)
> I think avoid to use mfn in the hypervisor interface is out-of-scope for
> this series. If we ever want to modify the Xen API in Linux, we should
> do in sync with Xen to avoid inconsistency on naming.
>
> Anyway, the oddity of mfn = pfn_to_gfn(...) is mostly contained in the
> x86 specific code. I don't mind to either add pfn_to_mfn and use it or
> add a comment /* PV-specific so mfn == gfn */ for every use of mfn =
> pfn_to_gfn(...).

I think the former is better (even thought it adds a test)

-boris