s390x/kvm: enable/reset cmma via vm attributes

Exploit the new api for userspace-controlled cmma. If supported, enable
cmma during kvm initialization and register a reset handler for cmma,
which is also called directly from the load IPL code.

The reset functionality is needed to reset the cmma state of the guest
pages, e.g. if a system reset is triggered via qemu monitor; otherwise
this could result in data corruption.

A guest triggered reboot may now lead to multiple cmma resets; this is
OK, however, as this is slowpath anyway and the simplest way to achieve
the intended effects.

Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>

target-s390x/cpu.h

@@ -1074,6 +1074,7 @@ void kvm_s390_enable_css_support(S390CPU *cpu);
 int kvm_s390_assign_subch_ioeventfd(EventNotifier *notifier, uint32_t sch,
                                     int vq, bool assign);
 int kvm_s390_cpu_restart(S390CPU *cpu);
+void kvm_s390_clear_cmma_callback(void *opaque);
 #else
 static inline void kvm_s390_io_interrupt(S390CPU *cpu,
                                         uint16_t subchannel_id,
@@ -1098,8 +1099,19 @@ static inline int kvm_s390_cpu_restart(S390CPU *cpu)
 {
     return -ENOSYS;
 }
+static inline void kvm_s390_clear_cmma_callback(void *opaque)
+{
+}
 #endif
 
+static inline void cmma_reset(S390CPU *cpu)
+{
+    if (kvm_enabled()) {
+        CPUState *cs = CPU(cpu);
+        kvm_s390_clear_cmma_callback(cs->kvm_state);
+    }
+}
+
 static inline int s390_cpu_restart(S390CPU *cpu)
 {
     if (kvm_enabled()) {

target-s390x/kvm.c

@@ -32,6 +32,7 @@
 #include "qemu/timer.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/kvm.h"
+#include "hw/hw.h"
 #include "cpu.h"
 #include "sysemu/device_tree.h"
 #include "qapi/qmp/qjson.h"
@@ -104,10 +105,67 @@ static int cap_async_pf;
 
 static void *legacy_s390_alloc(size_t size);
 
+static int kvm_s390_check_clear_cmma(KVMState *s)
+{
+    struct kvm_device_attr attr = {
+        .group = KVM_S390_VM_MEM_CTRL,
+        .attr = KVM_S390_VM_MEM_CLR_CMMA,
+    };
+
+    return kvm_vm_ioctl(s, KVM_HAS_DEVICE_ATTR, &attr);
+}
+
+static int kvm_s390_check_enable_cmma(KVMState *s)
+{
+    struct kvm_device_attr attr = {
+        .group = KVM_S390_VM_MEM_CTRL,
+        .attr = KVM_S390_VM_MEM_ENABLE_CMMA,
+    };
+
+    return kvm_vm_ioctl(s, KVM_HAS_DEVICE_ATTR, &attr);
+}
+
+void kvm_s390_clear_cmma_callback(void *opaque)
+{
+    int rc;
+    KVMState *s = opaque;
+    struct kvm_device_attr attr = {
+        .group = KVM_S390_VM_MEM_CTRL,
+        .attr = KVM_S390_VM_MEM_CLR_CMMA,
+    };
+
+    rc = kvm_vm_ioctl(s, KVM_SET_DEVICE_ATTR, &attr);
+    trace_kvm_clear_cmma(rc);
+}
+
+static void kvm_s390_enable_cmma(KVMState *s)
+{
+    int rc;
+    struct kvm_device_attr attr = {
+        .group = KVM_S390_VM_MEM_CTRL,
+        .attr = KVM_S390_VM_MEM_ENABLE_CMMA,
+    };
+
+    if (kvm_s390_check_enable_cmma(s) || kvm_s390_check_clear_cmma(s)) {
+        return;
+    }
+
+    rc = kvm_vm_ioctl(s, KVM_SET_DEVICE_ATTR, &attr);
+    if (!rc) {
+        qemu_register_reset(kvm_s390_clear_cmma_callback, s);
+    }
+    trace_kvm_enable_cmma(rc);
+}
+
 int kvm_arch_init(KVMState *s)
 {
     cap_sync_regs = kvm_check_extension(s, KVM_CAP_SYNC_REGS);
     cap_async_pf = kvm_check_extension(s, KVM_CAP_ASYNC_PF);
+
+    if (kvm_check_extension(s, KVM_CAP_VM_ATTRIBUTES)) {
+        kvm_s390_enable_cmma(s);
+    }
+
     if (!kvm_check_extension(s, KVM_CAP_S390_GMAP)
         || !kvm_check_extension(s, KVM_CAP_S390_COW)) {
         phys_mem_set_alloc(legacy_s390_alloc);

target-s390x/misc_helper.c

@@ -136,6 +136,7 @@ static int modified_clear_reset(S390CPU *cpu)
     pause_all_vcpus();
     cpu_synchronize_all_states();
     cpu_full_reset_all();
+    cmma_reset(cpu);
     io_subsystem_reset();
     scc->load_normal(CPU(cpu));
     cpu_synchronize_all_post_reset();
@@ -150,6 +151,7 @@ static int load_normal_reset(S390CPU *cpu)
     pause_all_vcpus();
     cpu_synchronize_all_states();
     cpu_reset_all();
+    cmma_reset(cpu);
     io_subsystem_reset();
     scc->initial_cpu_reset(CPU(cpu));
     scc->load_normal(CPU(cpu));

trace-events

@@ -1258,3 +1258,7 @@ xen_pv_mmio_write(uint64_t addr) "WARNING: write to Xen PV Device MMIO space (ad
 # hw/pci/pci_host.c
 pci_cfg_read(const char *dev, unsigned devid, unsigned fnid, unsigned offs, unsigned val) "%s %02u:%u @0x%x -> 0x%x"
 pci_cfg_write(const char *dev, unsigned devid, unsigned fnid, unsigned offs, unsigned val) "%s %02u:%u @0x%x <- 0x%x"
+
+# target-s390x/kvm.c
+kvm_enable_cmma(int rc) "CMMA: enabling with result code %d"
+kvm_clear_cmma(int rc) "CMMA: clearing with result code %d"