Re: [PATCH v4.14 1/4] KVM: PPC: Book3S HV: Fix trap number return from __kvmppc_vcore_entry

[Greg KH <greg@kroah.com>]

On Fri, May 11, 2018 at 04:19:06PM +1000, Paul Mackerras wrote:
> commit a8b48a4dccea77e29462e59f1dbf0d5aa1ff167c upstream.
> 
> This fixes a bug where the trap number that is returned by
> __kvmppc_vcore_entry gets corrupted.  The effect of the corruption
> is that IPIs get ignored on POWER9 systems when the IPI is sent via
> a doorbell interrupt to a CPU which is executing in a KVM guest.
> The effect of the IPI being ignored is often that another CPU locks
> up inside smp_call_function_many() (and if that CPU is holding a
> spinlock, other CPUs then lock up inside raw_spin_lock()).
> 
> The trap number is currently held in register r12 for most of the
> assembly-language part of the guest exit path.  In that path, we
> call kvmppc_subcore_exit_guest(), which is a C function, without
> restoring r12 afterwards.  Depending on the kernel config and the
> compiler, it may modify r12 or it may not, so some config/compiler
> combinations see the bug and others don't.
> 
> To fix this, we arrange for the trap number to be stored on the
> stack from the point where kvmhv_commence_exit is called until the
> end of the function, then the trap number is loaded and returned in
> r12 as before.
> 
> Cc: stable@vger.kernel.org # v4.8+
> Fixes: fd7bacbca47a ("KVM: PPC: Book3S HV: Fix TB corruption in guest exit path on HMI interrupt")
> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
> ---
>  arch/powerpc/kvm/book3s_hv_rmhandlers.S | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)

Now applied, thanks.


greg k-h