[PATCH 4/8] arm64: Add EL2 switch to soft_restart

[geoff@infradead.org (Geoff Levand)]

Hi Mark,

On Mon, 2015-01-26 at 19:02 +0000, Mark Rutland wrote:
> On Sat, Jan 17, 2015 at 12:23:34AM +0000, Geoff Levand wrote:
> > When a CPU is reset it needs to be put into the exception level it had when it
> > entered the kernel.  Update cpu_reset() to accept an argument el2_switch which
> > signals cpu_reset() to enter the soft reset address at EL2.  If el2_switch is
> > not set the soft reset address will be entered at EL1.
> > 
> > Update cpu_soft_restart() and soft_restart() to pass the return of
> > is_hyp_mode_available() as the el2_switch value to cpu_reset().  Also update the
> > comments of cpu_reset(), cpu_soft_restart() and soft_restart() to reflect this
> > change.
> > 
> > Signed-off-by: Geoff Levand <geoff@infradead.org>
> > ---
> >  arch/arm64/include/asm/proc-fns.h |  4 ++--
> >  arch/arm64/kernel/process.c       | 10 ++++++++-
> >  arch/arm64/mm/proc.S              | 47 +++++++++++++++++++++++++++++----------
> >  3 files changed, 46 insertions(+), 15 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/proc-fns.h b/arch/arm64/include/asm/proc-fns.h
> > index 9a8fd84..339394d 100644
> > --- a/arch/arm64/include/asm/proc-fns.h
> > +++ b/arch/arm64/include/asm/proc-fns.h
> > @@ -32,8 +32,8 @@ extern void cpu_cache_off(void);
> >  extern void cpu_do_idle(void);
> >  extern void cpu_do_switch_mm(unsigned long pgd_phys, struct mm_struct *mm);
> >  extern void cpu_reset(unsigned long addr) __attribute__((noreturn));
> > -void cpu_soft_restart(phys_addr_t cpu_reset,
> > -		unsigned long addr) __attribute__((noreturn));
> > +void cpu_soft_restart(phys_addr_t cpu_reset, unsigned long el2_switch,
> > +		      unsigned long addr) __attribute__((noreturn));
> >  extern void cpu_do_suspend(struct cpu_suspend_ctx *ptr);
> >  extern u64 cpu_do_resume(phys_addr_t ptr, u64 idmap_ttbr);
> >  
> > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> > index fde9923..371bbf1 100644
> > --- a/arch/arm64/kernel/process.c
> > +++ b/arch/arm64/kernel/process.c
> > @@ -50,6 +50,7 @@
> >  #include <asm/mmu_context.h>
> >  #include <asm/processor.h>
> >  #include <asm/stacktrace.h>
> > +#include <asm/virt.h>
> >  
> >  #ifdef CONFIG_CC_STACKPROTECTOR
> >  #include <linux/stackprotector.h>
> > @@ -60,7 +61,14 @@ EXPORT_SYMBOL(__stack_chk_guard);
> >  void soft_restart(unsigned long addr)
> >  {
> >  	setup_mm_for_reboot();
> > -	cpu_soft_restart(virt_to_phys(cpu_reset), addr);
> > +
> > +	/* TODO: Remove this conditional when KVM can support CPU restart. */
> > +	if (IS_ENABLED(CONFIG_KVM))
> > +		cpu_soft_restart(virt_to_phys(cpu_reset), 0, addr);
> 
> If we haven't torn down KVM, doesn't that mean that KVM is active at EL2
> (with MMU and caches on) at this point?
> 
> If that's the case then we cannot possibly try to call kexec(), because
> we cannot touch the memory used by the page tables for those EL2
> mappings. Things will explode if we do.

This conditional is just if KVM, do things the old way (don't try to
switch exception levels).  It is to handle the system shutdown case.

Another patch in this series '[PATCH 7/8] arm64/kexec: Add checks for
KVM' assures kexec cannot happen when KVM is configured.

-Geoff