Re: [PATCH 11/14] xen/x86: mm: Re-implement set_gpfn_from_mfn() as a static inline function

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

Hi,

On 10/05/2019 14:48, Jan Beulich wrote:
>>>> On 10.05.19 at 15:41, <julien.grall@arm.com> wrote:
>> On 10/05/2019 14:35, Jan Beulich wrote:
>>>>>> On 10.05.19 at 15:27, <julien.grall@arm.com> wrote:
>>>> On 10/05/2019 13:43, Jan Beulich wrote:
>>>>>>>> On 07.05.19 at 17:14, <julien.grall@arm.com> wrote:
>>>>>> +static inline void set_gpfn_from_mfn(unsigned long mfn, unsigned long pfn)
>>>>>> +{
>>>>>> +    struct domain *d = page_get_owner(mfn_to_page(_mfn(mfn)));
>>>>>> +    unsigned long entry = (d && (d == dom_cow)) ? SHARED_M2P_ENTRY : pfn;
>>>>>
>>>>> The && here looks, ehm, funny, but I guess it's needed for early boot?
>>>>
>>>> I have no idea, this is x86 not Arm...
>>>>
>>>>> But that's perhaps a separate thing to clean up. However, looking at
>>>>> this - why is Arm setting up dom_cow in the first place?
>>>>
>>>> Common code is using dom_cow, so I don't think we want it to be NULL on Arm to
>>>> avoid weird issues.
>>>
>>> I didn't mean it to remain NULL. Common code doesn't dereference it
>>> (and isn't supposed to), so I'd consider initializing it to some known
>>> faulting non-NULL address, if there is such on Arm.
>>
>> Patches are welcomed ;).
> 
> So is there such an address on Arm?

0 - 2MB is unmapped so far. I don't know whether this will still be the case (at 
least for the range 4KB - 2MB) with the rework I am attempting.

Cheers,

-- 
Julien Grall

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