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>

5 files changed, 40 insertions, 2 deletions

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 962b92e6cf00..9a809f935580 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -71,7 +71,10 @@ struct kvm_s390_sie_block {
         __u8    reserved08[4];          /* 0x0008 */
 #define PROG_IN_SIE (1<<0)
         __u32   prog0c;                 /* 0x000c */
-        __u8    reserved10[24];         /* 0x0010 */
+        __u8    reserved10[16];         /* 0x0010 */
+#define PROG_BLOCK_SIE 0x00000001
+        atomic_t prog20;                /* 0x0020 */
+        __u8    reserved24[4];          /* 0x0024 */
         __u64   cputm;                  /* 0x0028 */
         __u64   ckc;                    /* 0x0030 */
         __u64   epoch;                  /* 0x0038 */
diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index 6456bbe1fbb1..78db6338695d 100644
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -163,6 +163,7 @@ int main(void)
         DEFINE(__THREAD_trap_tdb, offsetof(struct task_struct, thread.trap_tdb));
         DEFINE(__GMAP_ASCE, offsetof(struct gmap, asce));
         DEFINE(__SIE_PROG0C, offsetof(struct kvm_s390_sie_block, prog0c));
+        DEFINE(__SIE_PROG20, offsetof(struct kvm_s390_sie_block, prog20));
 #endif /* CONFIG_32BIT */
         return 0;
 }
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:
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index c1c7c683fa26..ef4ef21f2c73 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -454,6 +454,34 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
         return 0;
 }
 
+void s390_vcpu_block(struct kvm_vcpu *vcpu)
+{
+        atomic_set_mask(PROG_BLOCK_SIE, &vcpu->arch.sie_block->prog20);
+}
+
+void s390_vcpu_unblock(struct kvm_vcpu *vcpu)
+{
+        atomic_clear_mask(PROG_BLOCK_SIE, &vcpu->arch.sie_block->prog20);
+}
+
+/*
+ * Kick a guest cpu out of SIE and wait until SIE is not running.
+ * If the CPU is not running (e.g. waiting as idle) the function will
+ * return immediately. */
+void exit_sie(struct kvm_vcpu *vcpu)
+{
+        atomic_set_mask(CPUSTAT_STOP_INT, &vcpu->arch.sie_block->cpuflags);
+        while (vcpu->arch.sie_block->prog0c & PROG_IN_SIE)
+                cpu_relax();
+}
+
+/* Kick a guest cpu out of SIE and prevent SIE-reentry */
+void exit_sie_sync(struct kvm_vcpu *vcpu)
+{
+        s390_vcpu_block(vcpu);
+        exit_sie(vcpu);
+}
+
 int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
 {
         /* kvm common code refers to this, but never calls it */
diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index efc14f687265..7a8abfd26a0f 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -133,6 +133,10 @@ int kvm_s390_handle_sigp(struct kvm_vcpu *vcpu);
 /* implemented in kvm-s390.c */
 int kvm_s390_vcpu_store_status(struct kvm_vcpu *vcpu,
                                  unsigned long addr);
+void s390_vcpu_block(struct kvm_vcpu *vcpu);
+void s390_vcpu_unblock(struct kvm_vcpu *vcpu);
+void exit_sie(struct kvm_vcpu *vcpu);
+void exit_sie_sync(struct kvm_vcpu *vcpu);
 /* implemented in diag.c */
 int kvm_s390_handle_diag(struct kvm_vcpu *vcpu);