Re: [uml-devel] userfaultfd for UML userspace processes

[Anton I. <ant...@ko...>]

Am I right that this may be a route to avoid the full munmap we have presently upon exec or I am missing something.  If that is the case it will be well worth it.

On 13 May 2017 11:24:04 GMT+01:00, Thomas Meyer <th...@m3...> wrote:
>Am 13.05.2017 um 12:04 schrieb Richard Weinberger:
>> Thomas,
>
>Hi,
>
>> On Sat, May 13, 2017 at 10:10 AM, Thomas Meyer <th...@m3...>
>wrote:
>>>
>>> Hi,
>>>
>>> after looking into using userfaultfd for the userspace UML process
>>> page fault handling, I come to the conclusion that userfaultfd
>>> *cannot* be used for above goal as it only operates on mmaped memory
>>> areas.
>>> Am I missing something? What do you think about it?
>> 
>> See: https://lkml.org/lkml/2015/5/20/541
>Cool! Thanks for the hint. I don't follow LKML, so...
>
>But Andrea wrote:
>
>"Alternatively once we extend the handle_userfault to tmpfs you could
>map the page in two virtual mappings and track the faults in one
>mapping (where the tracked app runs) and read/write the page contents
>in the other mapping that isn't tracked by the userfault."
>
>I think this is now the case with 4.11, isn't it?
>
>As I understand this we must do the following:
>
>kernel process: Map a tmpfs region for each userspace process with 
>read/write.
>userspace process: Map the same tmpfs for the current process and 
>userfaultfd the whole address space, and give the userfaultfd fd to the
>
>kernel somehow and process the page fault there and fill/copy the 
>faulted page accordingly.
>
>so each userspace process would be backed by a tmpfs mmap region? sound
>
>complicated.
>
>with kind regards
>thomas
>
>
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