s390/kvm: Provide a way to prevent reentering SIE

Lets provide functions to prevent KVM from reentering SIE and
to kick cpus out of SIE. We cannot use the common kvm_vcpu_kick code,
since we need to kick out guests in places that hold architecture
specific locks (e.g. pgste lock) which might be necessary on the
other cpus - so no waiting possible.

So lets provide a bit in a private field of the sie control block
that acts as a gate keeper, after we claimed we are in SIE.
Please note that we do not reuse prog0c, since we want to access
that bit without atomic ops.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/s390/kernel/entry64.S b/arch/s390/kernel/entry64.S
index c2e81b4ea42c..c7daeefb9864 100644
--- a/arch/s390/kernel/entry64.S
+++ b/arch/s390/kernel/entry64.S
@@ -958,7 +958,9 @@ sie_loop:
         lctlg   %c1,%c1,__GMAP_ASCE(%r14)       # load primary asce
 sie_gmap:
         lg      %r14,__SF_EMPTY(%r15)           # get control block pointer
-        oi      __SIE_PROG0C+3(%r14),1          # we are in SIE now
+        oi      __SIE_PROG0C+3(%r14),1          # we are going into SIE now
+        tm      __SIE_PROG20+3(%r14),1          # last exit...
+        jnz     sie_done
         LPP     __SF_EMPTY(%r15)                # set guest id
         sie     0(%r14)
 sie_done: