Kexec on arm64

[geoff@infradead.org (Geoff Levand)]

Hi,

On Mon, 2014-07-28 at 16:38 +0100, Mark Rutland wrote:
> On Mon, Jul 28, 2014 at 04:00:18PM +0100, Arun Chandran wrote:
> > I have these changes to the code.
> >         flush_icache_range((unsigned long)reboot_code_buffer,
> > -               relocate_new_kernel_size);
> > +               (unsigned long)(reboot_code_buffer + relocate_new_kernel_size));

Thanks, I introduced this in my last version in an attempt to clean up
the code, but on studying setup_restart(), I wonder if we even need to
do this icache flush here (see below).

> >         /*
> >          * Flush any data used by relocate_new_kernel in preparation for
> > #########
> > Passing of second variable to flush_icache_range() is wrong
> > it expects an address not length.
> 
> A simpler option would be to nuke the entire icache before branching to
> the new image.

flush_cache_all(), which is called by setup_restart(), does a 'ic
ialluis'.  The ARM says that this will invalidate all instruction caches
for the inner shareable domain.  Do we need something more?

> > 2)
> > 
> > #######
> > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> > index 9ed7327..e3fc8d6 100644
> > --- a/arch/arm64/kernel/process.c
> > +++ b/arch/arm64/kernel/process.c
> > 
> > @@ -84,12 +91,17 @@ void soft_restart(unsigned long addr)
> >  {
> >         typedef void (*phys_reset_t)(unsigned long);
> >         phys_reset_t phys_reset;
> > +       unsigned long jump_addr = addr;
> > +
> > +       phys_reset = (phys_reset_t)virt_to_phys(cpu_reset);
> > +
> > +       __flush_dcache_area(&jump_addr, 8);
> > +       __flush_dcache_area(&phys_reset, 8);
> 
> Are these values really not getting stashed in registers?

Looking at the disassembled code of soft_restart() from my compiler,
addr is being saved on the stack over the call to setup_restart(), which
I would expect it to do.

> If the compiler is spilling, then we have absolutely no guarantee about
> any part of the stack. If that's the case, then we can't use the stack
> at all. These need to be rewritten in asm if the compiler is spilling.

I think we just need to put the restart addr in a variable and flush
that to the PoC.

Arun, I pushed out a fixed version of soft_restart(), so please try
another UP + L3 boot.

-Geoff