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Re: [Xen-devel] [PATCH] x86: fix determination of bit count for struct domain allocations

On 14/03/14 16:12, Jan Beulich wrote:
>>>> On 14.03.14 at 16:51, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 14/03/14 15:46, Jan Beulich wrote:
>>>>>> On 14.03.14 at 16:30, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> On 14/03/14 15:23, Jan Beulich wrote:
>>>>> We can't just add in the hole shift value, as the hole may be at or
>>>>> above the 44-bit boundary. Instead we need to determine the total bit
>>>>> count until reaching 32 significant (not squashed out) bits in PFN
>>>>> representations.
>>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>>> --- a/xen/arch/x86/domain.c
>>>>> +++ b/xen/arch/x86/domain.c
>>>>> @@ -180,6 +180,19 @@ void dump_pageframe_info(struct domain *
>>>>>      spin_unlock(&d->page_alloc_lock);
>>>>>  }
>>>>> +static unsigned int __init noinline _domain_struct_bits(void)
>>>> noinline for debugging purposes?
>>> No, for it to really end up in .init.text (as the caller is in .text).
>> In which case it should assert/bug if the function returns 0, to be sure
>> we will never fall into the unlikely case again and try to call it from
>> a non-init function.  Also a comment to explain this.
> I really dislike asserting the absolutely obvious: The function can
> be very easily proven to only return values in the range [44,64].
> Jan

Hmm ok, but at the very least this deserves a comment to that effect.


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