Re: Xen MP panics in cpu_switchto()

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Mon, Jan 13, 2020 at 06:33:08PM +0000, Andrew Doran wrote:
> On Mon, Jan 13, 2020 at 05:43:51PM +0100, Manuel Bouyer wrote:
> 
> > On Mon, Jan 13, 2020 at 04:59:50PM +0100, Manuel Bouyer wrote:
> > > It also sets rsp and rbp. I think rbp is not set by anything else, at last
> > > in the Xen case.
> > > The different rbp value would explain why in one case we hit a KASSERT()
> > > in lwp_startup later.
> > > But I don't know what pcb_rbp contains; I couldn't find where the pcb for
> > > idlelwp is initialized.
> > 
> > I tried the attached patch, which should set rsp/rbp as cpu_switchto()
> > does. It doens't cause the lwp_startup() KASSERT as calling cpu_switchto()
> > does; it also doesn't change the scheduler behavior.
> 
> Wait - do you mean that everything works now?  Or that everything still runs
> on CPU0?

No, everything still runs on CPU0

> 
> The very first thing that idle_loop() does on amd64/i386 is set up the frame
> pointer - ebp/rbp.
> 
> 0000000000000000 <idle_loop>:
>    0:   55                      push   %rbp
>    1:   48 89 e5                mov    %rsp,%rbp
>    4:   41 56                   push   %r14
>    6:   41 55                   push   %r13

OK, so it's OK that my patch doesn't changes anything.
And so I still don't understand the KASSERT when cpu_switchto() is called
before idle_loop().

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--