Re: [PATCH v1 04/12] xen/hvmlite: Bootstrap HVMlite guest

[Boris Ostrovsky]

On 01/26/2016 01:46 PM, Andy Lutomirski wrote:
> On Tue, Jan 26, 2016 at 10:34 AM, Luis R. Rodriguez <mcgrof@xxxxxxxx> wrote:
> > On Mon, Jan 25, 2016 at 05:28:08PM -0500, Boris Ostrovsky wrote:
> > > On 01/25/2016 04:21 PM, H. Peter Anvin wrote:
> > > > On 01/25/16 13:12, Luis R. Rodriguez wrote:
> > > > > > Perhaps, but someone would still have to set hardware_subarch. And
> > > > > > it's hvmlite_bootparams() that does it.
> > > > > No, Xen would do it as well, essentially all of hvmlite_bootparams() could be
> > > > > done in Xen.
> > > > Or a stub code.
> > > This patch in fact is the stub for Xen HVMlite guests, after we are
> > > done with it we jump to bare-metal startup code (i.e startup_32|64)
> > Right the point is the stub need not be in Linux, I'll explain in the other
> > thread where I provided more details on the different known approaches.
> ISTM if the Xen ABI-specified entry point has a different convention
> than the Linux native entry, then the stub should live in Linux.  It
> would be just a couple if lines of code, right?

It's not exactly a couple of lines but it's not large neither. It mainly 
sets up boot_params (similar to what make_boot_params() does for EFI). 
Plus, for 64-bit, it loads identity page tables and switches to long 
mode. And then jumps to bare-meta startup code.


> The issue that caused headaches in the past isn't that there's code
> that's executed only on native, it's that there are whole big
> functions that are executed only on native for no good reason and that
> aren't clearly marked.

This won't happen with HVMlite.

> If we had native_start_kernel and xen_start_kernel, and they both
> called very quickly in to common_start_kernel, it would be very clear
> what's going on.

What is now xen_start_kernel() is no longer the entry point for HVMlite. 
It is called as x86_init.oem.arch_setup() (or I may even move it to 
x86_hyper_xen.init_platform() or something like that).

-boris