Re: PAE support for kvm(3)

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

On Fri, 01 Oct 2010 02:35:22 +0200, Jean-Yves Migeon
<jeanyves.migeon%free.fr@localhost> wrote:
> Hi list,
> 
> Attached is the patch required to add PAE support in kvm(3). Except for
> one "major" nit (see below), it seems to be functional: I can sync a
> kernel, with or without PAE enabled, and all libkvm binaries (vmstat(1),
> netstat(1), ...) still work on the core files.
> [snip]
> However, I have some kind of "chicken-egg" situation there: getting
> i386_use_pae value needs a go through KREAD/kvm_read, but these
> functions cannot work properly until the correct kvatop function has
> been selected. Downside is, this depends on i386_use_pae value...
> 
> At this late hour, I cannot think of a quick and clean solution. Adding
> an element to the cpu_kcore_hdr_t will break all core dumps from before
> the change (the offset of the memory segments, "memsegs", will differ);
> that would need compat code to cope with that. Another possibility is to
> set the last bit in pdppaddr to indicate PAE activation, but, this seems
> like a dirty hack (I don't think that PDPpaddr will ever go that high
> though).
> 
> Any advice for that one? Thanks in advance!

Replying to myself:

Having some sleep seems to help: as the pdppaddr is at least 32 bits
aligned (least common multiple between PAE and !PAE),
that gives me some bits accessible which are not used by the translation
code.

So I think I will use one to signify "use PAE."

Cheers,

-- 
Jean-Yves Migeon
jeanyves.migeon%free.fr@localhost