s390x: introduce s390_get_memory_limit()

Let's add s390_get_memory_limit(), to query what has been successfully
set via s390_set_memory_limit(). Allow setting the limit only once.

We'll remember the limit in the machine state. Move
s390_set_memory_limit() to machine code, merging it into
set_memory_limit(), because this really is a machine property.

Message-ID: <20241219144115.2820241-7-david@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>

hw/s390x/s390-virtio-ccw.c

@@ -45,6 +45,7 @@
 #include "migration/blocker.h"
 #include "qapi/visitor.h"
 #include "hw/s390x/cpu-topology.h"
+#include "kvm/kvm_s390x.h"
 #include CONFIG_DEVICES
 
 static Error *pv_mig_blocker;
@@ -121,12 +122,16 @@ static void subsystem_reset(void)
     }
 }
 
-static void set_memory_limit(uint64_t new_limit)
+static void s390_set_memory_limit(S390CcwMachineState *s390ms,
+                                  uint64_t new_limit)
 {
-    uint64_t hw_limit;
-    int ret;
+    uint64_t hw_limit = 0;
+    int ret = 0;
 
-    ret = s390_set_memory_limit(new_limit, &hw_limit);
+    assert(!s390ms->memory_limit && new_limit);
+    if (kvm_enabled()) {
+        ret = kvm_s390_set_mem_limit(new_limit, &hw_limit);
+    }
     if (ret == -E2BIG) {
         error_report("host supports a maximum of %" PRIu64 " GB",
                      hw_limit / GiB);
@@ -135,10 +140,12 @@ static void set_memory_limit(uint64_t new_limit)
         error_report("setting the guest size failed");
         exit(EXIT_FAILURE);
     }
+    s390ms->memory_limit = new_limit;
 }
 
 static void s390_memory_init(MachineState *machine)
 {
+    S390CcwMachineState *s390ms = S390_CCW_MACHINE(machine);
     MemoryRegion *sysmem = get_system_memory();
     MemoryRegion *ram = machine->ram;
     uint64_t ram_size = memory_region_size(ram);
@@ -154,7 +161,7 @@ static void s390_memory_init(MachineState *machine)
         exit(EXIT_FAILURE);
     }
 
-    set_memory_limit(ram_size);
+    s390_set_memory_limit(s390ms, ram_size);
 
     /* Map the initial memory. Must happen after setting the memory limit. */
     memory_region_add_subregion(sysmem, 0, ram);

include/hw/s390x/s390-virtio-ccw.h

@@ -29,10 +29,18 @@ struct S390CcwMachineState {
     bool dea_key_wrap;
     bool pv;
     uint8_t loadparm[8];
+    uint64_t memory_limit;
 
     SCLPDevice *sclp;
 };
 
+static inline uint64_t s390_get_memory_limit(S390CcwMachineState *s390ms)
+{
+    /* We expect to be called only after the limit was set. */
+    assert(s390ms->memory_limit);
+    return s390ms->memory_limit;
+}
+
 #define S390_PTF_REASON_NONE (0x00 << 8)
 #define S390_PTF_REASON_DONE (0x01 << 8)
 #define S390_PTF_REASON_BUSY (0x02 << 8)

target/s390x/cpu-sysemu.c

@@ -255,14 +255,6 @@ unsigned int s390_cpu_set_state(uint8_t cpu_state, S390CPU *cpu)
     return s390_count_running_cpus();
 }
 
-int s390_set_memory_limit(uint64_t new_limit, uint64_t *hw_limit)
-{
-    if (kvm_enabled()) {
-        return kvm_s390_set_mem_limit(new_limit, hw_limit);
-    }
-    return 0;
-}
-
 void s390_set_max_pagesize(uint64_t pagesize, Error **errp)
 {
     if (kvm_enabled()) {

target/s390x/cpu.h

@@ -881,7 +881,6 @@ static inline void s390_do_cpu_load_normal(CPUState *cs, run_on_cpu_data arg)
 
 /* cpu.c */
 void s390_crypto_reset(void);
-int s390_set_memory_limit(uint64_t new_limit, uint64_t *hw_limit);
 void s390_set_max_pagesize(uint64_t pagesize, Error **errp);
 void s390_cmma_reset(void);
 void s390_enable_css_support(S390CPU *cpu);