Re: [PATCH Part2 RFC v4 10/40] x86/fault: Add support to handle the RMP fault for user address

[Dave Hansen]

On 7/12/21 9:11 AM, Brijesh Singh wrote:
>> Please fix this code to handle hugetlbfs along with any other non-THP
>> source of level>0 mappings.  DAX comes to mind.  "Handle" can mean
>> rejecting these.  You don't have to find some way to split them and make
>> the VM work, just fail safely, ideally as early as possible.
>>
>> To me, this is a fundamental requirement before this code can be
>> accepted.
> 
> Understood, if userspace decided to use the hugetlbfs backing pages then
> I believe earliest we can detect is when we go about adding the pages in
> the RMP table. I'll add a check, and fail the page state change.

Really?  You had to feed the RMP entries from *some* mapping in the
first place.  Is there a reason the originating mapping can't be checked
at that point instead of waiting for the fault?