Re: [PATCH] xen/x86: Adjust stack pointer in xen_sysexit

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 11/16/2015 02:03 PM, Andy Lutomirski wrote:
> It's still a waste of effort, though. Also, I'd eventually like the 
> number of places in Xen code in which rsp/esp is invalid to be exactly 
> zero, and this approach makes this harder or even impossible.

That's what PVH is going to do.



> Does PVH hook into the entry asm code at all?  I thought it was just
> boot code and drivers.

Not the current version --- it starts with xen_start_kernel(). But we 
are currently changing it and my plan is to have a small stub executed 
initially (to set bootparams and such) and then jump to startup_{32|64}().

>
> In any case, someone needs to do some serious review and cleanup on
> the whole paravirt op mess.  We have a bunch of paravirt ops that
> serve little purpose.
>
> The paravirt infrastructure is a bit weird, too: it seems to
> effectively have four states for each patch site.  There's:
>
> 1. The initial state, which is unoptimized and works on native.
> Presumably any of these that happen early also need to work, if
> slowly, on Xen.

Not on PV (and as of today, on PVH) --- we start directly from 
xen_start_kernel(). I.e.  from step 2.

>
> 2. The Xen state without text patching.  I'm not actually sure why
> this exists at all.  Are there pvops that need to switch too early for
> us to patch the text?

I don't think so.

-boris