[PATCH v4] s390: kvm: adjust diag318 resets to retain data

[Collin Walling]

The CPNC portion of the diag318 data is erroneously reset during an
initial CPU reset caused by SIGP. Let's go ahead and relocate the
diag318_info field within the CPUS390XState struct such that it is
only zeroed during a clear reset. This way, the CPNC will be retained
for each VCPU in the configuration after the diag318 instruction
has been invoked.

The s390_machine_reset code already takes care of zeroing the diag318
data on VM resets, which also cover resets caused by diag308.

Signed-off-by: Collin Walling <walling@linux.ibm.com>
Fixes: fabdada9357b ("s390: guest support for diagnose 0x318")
Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com> 
---

Changelog:

    v4
    - fixed up commit message and added r-b's

    v3
    - reverted changes from previous versions
    - simply relocate diag318_info in CPU State struct
    - add comment in set_diag318 to explain resets

    v2
    - handler uses run_on_cpu again
    - reworded commit message slightly
    - added fixes and reported-by tags 

    v3
    - nixed code reduction changes
    - added a comment to diag318 handler to briefly describe
        when relevent data is zeroed

---
 target/s390x/cpu.h     | 4 ++--
 target/s390x/kvm/kvm.c | 4 ++++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
index 3153d053e9..88aace36ff 100644
--- a/target/s390x/cpu.h
+++ b/target/s390x/cpu.h
@@ -63,6 +63,8 @@ struct CPUS390XState {
     uint64_t etoken;       /* etoken */
     uint64_t etoken_extension; /* etoken extension */
 
+    uint64_t diag318_info;
+
     /* Fields up to this point are not cleared by initial CPU reset */
     struct {} start_initial_reset_fields;
 
@@ -118,8 +120,6 @@ struct CPUS390XState {
     uint16_t external_call_addr;
     DECLARE_BITMAP(emergency_signals, S390_MAX_CPUS);
 
-    uint64_t diag318_info;
-
 #if !defined(CONFIG_USER_ONLY)
     uint64_t tlb_fill_tec;   /* translation exception code during tlb_fill */
     int tlb_fill_exc;        /* exception number seen during tlb_fill */
diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
index 5b1fdb55c4..6acf14d5ec 100644
--- a/target/s390x/kvm/kvm.c
+++ b/target/s390x/kvm/kvm.c
@@ -1585,6 +1585,10 @@ void kvm_s390_set_diag318(CPUState *cs, uint64_t 
diag318_info)
         env->diag318_info = diag318_info;
         cs->kvm_run->s.regs.diag318 = diag318_info;
         cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_DIAG318;
+        /*
+         * diag 318 info is zeroed during a clear reset and
+         * diag 308 IPL subcodes.
+         */
     }
 }
 
-- 
2.31.1