Jan Beulich wrote:
>>>> "Yang, Xiaowei" <xiaowei.yang@intel.com> 20.03.09 09:34 >>>
>> Jan Beulich wrote:
>>>>>> "Yang, Xiaowei" <xiaowei.yang@intel.com> 20.03.09 06:05 >>>
>>>> DIRECTMAP_VIRT_END can't be passed to virt_to_mfn(), as it's just beyond 
>>>> direct map boundary and triggers ASSERT very early at boot time.
>>> While I agree to the analysis, I would think that this
>>>
>>> +              mfn + needed <= virt_to_mfn(DIRECTMAP_VIRT_END - PAGE_SIZE) )
>>>
>>> should rather be
>>>
>>> +              mfn + needed <= virt_to_mfn(DIRECTMAP_VIRT_END - 1) + 1 )
>>>
>> virt_to_mfn(DIRECTMAP_VIRT_END - 1) is equal to 
> 
> Depending on whether DIRECTMAP_VIRT_END is the last byte or the first
> following byte. Using "- 1" avoids such a dependency.
> 
>> virt_to_mfn(DIRECTMAP_VIRT_END - PAGE_SIZE). Why +1? We use '<=' here.
> 
> Because on the left side of the comparison we also calculate the first
> following mfn, not the last included one.
> 
Jan,
Thanks for the clarification!

Now I found another potential issue. Since mfn+needed could be equal to 
virt_to_mfn(DIRECTMAP_VIRT_END-1)+1, it can't be passed to mfn_to_virt() 
directly - the valid range is [0,DIRECT_MAP_BYTES>>PAGE_SHIFT).

Here is the patch to fix it. More assert and 32 bit counterpart are added.

Signed-off-by: Xiaowei Yang <xiaowei.yang@intel.com>

Thanks,
xiaowei