• Paul Mackerras's avatar
    KVM: PPC: Book3S HV: Fix trap number return from __kvmppc_vcore_entry · b87943f3
    Paul Mackerras authored
    commit a8b48a4d 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 'guest_bypass:' label 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: fd7bacbc ("KVM: PPC: Book3S HV: Fix TB corruption in guest exit path on HMI interrupt")
    Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    
    b87943f3
book3s_hv_rmhandlers.S 68.7 KB