Re: [PATCH v4 12/16] xen/mm: Switch common/memory.c to use typesafe MFN

From: "Jan Beulich" <JBeulich@suse.com>
To: Julien Grall <julien.grall@arm.com>
Cc: Tim Deegan <tim@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	xen-devel@lists.xen.org
Subject: Re: [PATCH v4 12/16] xen/mm: Switch common/memory.c to use typesafe MFN
Date: Mon, 05 Mar 2018 07:41:54 -0700	[thread overview]
Message-ID: <5A9D654202000078001AE983@prv-mh.provo.novell.com> (raw)
In-Reply-To: <8a879538-9206-cc79-2951-69f89f53dbc1@arm.com>

>>> On 05.03.18 at 15:18, <julien.grall@arm.com> wrote:
> On 02/03/18 15:34, Jan Beulich wrote:
>>>>> On 21.02.18 at 15:02, <julien.grall@arm.com> wrote:
>>> @@ -95,11 +101,18 @@ static unsigned int max_order(const struct domain *d)
>>>       return min(order, MAX_ORDER + 0U);
>>>   }
>>>   
>>> +/* Helper to copy a typesafe MFN to guest */
>>> +#define copy_mfn_to_guest(hnd, off, mfn)            \
>>> +    ({                                              \
>>> +        xen_pfn_t mfn_ = mfn_x(mfn);                \
>>> +        __copy_to_guest_offset(hnd, off, &mfn_, 1); \
>>> +    })
>> 
>> Hmm, not really nice, but what do you do.
> 
> I am open to better suggestion. I wanted to avoid the conversion all 
> over the code.

I have no better suggestion, I'm sorry, hence the "but what do
you do."

> Also, do you have an opinion on Wei's suggestion:
> 
> "What I meant was to make copy_{to,from}_guest* type-safe. I just feel it
> a bit strange you only created a wrapper for this file. I wonder why.
> 
> Note I'm just asking question. That's not necessarily a good idea to
> turn them all in the end."

Well, I didn't really understand what he's after (in the context of
this series) - copy_{to,from}_guest() don't take or return MFNs or
GFNs.

Jan

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