----- Original Message -----
> Hi Dave,
>
> At 12/20/2017 02:15 AM, Dave Anderson wrote:
> >
> >
> > ----- Original Message -----
> >> Dear Dave,
> >>
> >> I saw your commit
> >>
> >> 307e7f35f510("First phase of future support for x86_64 5-level page
> >> tables.")
> >>
> >> in crash git-tree. It is the preparatory for x86_64 5-level page tables.
> >> There may be more things to be done to support for 5-level.
> >
> > Right. There needs to be a manner of determining very early on whether
> > the kernel page tables are using 5-level. And during crash runtime, there
> > needs to be a manner of determining whether each user-space task is using
> > 4- or 5-level page tables. Also, it may be possible/preferable to
> > squeeze the 5-level support into the currently existing x86_64_kvtop() and
> > x86_64_uvtop() functions instead of using the new xxx_5level() function
> > placeholders that I added in the preparatory patch.
> >
>
> It is really helpful to me.
>
> >>
> >> I hope to know:
> >>
> >> 1. What is the current state of the 5-level page table in Crash?
> >
> > I have done nothing further beyond than the preparatory steps in that
> > commit.
> >
> >>
> >> 2. If there are some reason that we should pause the support work of
> >> 5-level page tables currently.
> >
> > No, not really. I originally delayed further work because originally it
> > was enabled by kernel CONFIG, but as I understand it now, it is enabled by
> > a combination of a kernel CONFIG and a boot command line option? But
>
> I am sorry I just found the CONFIG_X86_5LEVEL, Could you tell me the
> name of boot command line option?
I thought I had seen a patch posted on LKML that enabled the boot command line option,
but according to the current Documentation/x86/x86_64/5level-paging.txt, it is still TBD:
$ cat Documentation/x86/x86_64/5level-page.txt
... [ cut ] ...
== Enabling 5-level paging ==
CONFIG_X86_5LEVEL=y enables the feature.
So far, a kernel compiled with the option enabled will be able to boot
only on machines that supports the feature -- see for 'la57' flag in
/proc/cpuinfo.
The plan is to implement boot-time switching between 4- and 5-level paging
in the future.
...
Dave
>
> > since I have never seen or worked with a kernel with it enabled, I've
>
> Indeed, we only can use it in QEmu now.
>
> > not done anything further.
>
> Yes, I see.
>
> >
> >>
> >> 3. Are you already doing it?
> >
> > No. Are you offering to complete the work?
> >
>
> Aha, I am willing to, But I am not familiar with crash, I will try me
> best to do it.
>
> Thanks,
> dou
>
>
>
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