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Re: [PATCH for-8.2] target/s390x/kvm: Simplify the GPRs, ACRs, CRs and p

From: Thomas Huth
Subject: Re: [PATCH for-8.2] target/s390x/kvm: Simplify the GPRs, ACRs, CRs and prefix synchronization code
Date: Mon, 28 Aug 2023 20:20:13 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 
On 14/08/2023 21.06, Thomas Huth wrote:

KVM_SYNC_GPRS, KVM_SYNC_ACRS, KVM_SYNC_CRS and KVM_SYNC_PREFIX are
available since kernel 3.10. Since we already require at least kernel
3.15 in the s390x KVM code, we can assume that the KVM_CAP_SYNC_REGS
sync code is always possible for these registers, and remove the
related checks and fallbacks via KVM_SET_REGS and KVM_GET_REGS.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
  target/s390x/kvm/kvm.c | 119 ++++++++++++-----------------------------
  1 file changed, 34 insertions(+), 85 deletions(-)


Ping! Anybody any comments on this one?

 Thomas


diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
index a9e5880349..ff415f7b30 100644
--- a/target/s390x/kvm/kvm.c
+++ b/target/s390x/kvm/kvm.c
@@ -148,7 +148,6 @@ const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
      KVM_CAP_LAST_INFO
  };
-static int cap_sync_regs; 
  static int cap_async_pf;
  static int cap_mem_op;
  static int cap_mem_op_extension;
@@ -342,21 +341,28 @@ static void ccw_machine_class_foreach(ObjectClass *oc, 
void *opaque)
int kvm_arch_init(MachineState *ms, KVMState *s) 
  {
+    int required_caps[] = {
+        KVM_CAP_DEVICE_CTRL,
+        KVM_CAP_SYNC_REGS,
+    };
+
+    for (int i = 0; i < ARRAY_SIZE(required_caps); i++) {
+        if (!kvm_check_extension(s, required_caps[i])) {
+            error_report("KVM is missing capability #%d - "
+                         "please use kernel 3.15 or newer", required_caps[i]);
+            return -1;
+        }
+    }
+
      object_class_foreach(ccw_machine_class_foreach, TYPE_S390_CCW_MACHINE,
                           false, NULL);
- if (!kvm_check_extension(kvm_state, KVM_CAP_DEVICE_CTRL)) { 
-        error_report("KVM is missing capability KVM_CAP_DEVICE_CTRL - "
-                     "please use kernel 3.15 or newer");
-        return -1;
-    }
      if (!kvm_check_extension(s, KVM_CAP_S390_COW)) {
          error_report("KVM is missing capability KVM_CAP_S390_COW - "
                       "unsupported environment");
          return -1;
      }
- cap_sync_regs = kvm_check_extension(s, KVM_CAP_SYNC_REGS); 
      cap_async_pf = kvm_check_extension(s, KVM_CAP_ASYNC_PF);
      cap_mem_op = kvm_check_extension(s, KVM_CAP_S390_MEM_OP);
      cap_mem_op_extension = kvm_check_extension(s, 
KVM_CAP_S390_MEM_OP_EXTENSION);
@@ -463,15 +469,15 @@ void kvm_s390_reset_vcpu_normal(S390CPU *cpu)
static int can_sync_regs(CPUState *cs, int regs) 
  {
-    return cap_sync_regs && (cs->kvm_run->kvm_valid_regs & regs) == regs;
+    return (cs->kvm_run->kvm_valid_regs & regs) == regs;
  }
int kvm_arch_put_registers(CPUState *cs, int level) 
  {
+    const int required_syncs = KVM_SYNC_GPRS | KVM_SYNC_ACRS |
+                               KVM_SYNC_CRS | KVM_SYNC_PREFIX;
      S390CPU *cpu = S390_CPU(cs);
      CPUS390XState *env = &cpu->env;
-    struct kvm_sregs sregs;
-    struct kvm_regs regs;
      struct kvm_fpu fpu = {};
      int r;
      int i;
@@ -480,21 +486,16 @@ int kvm_arch_put_registers(CPUState *cs, int level)
      cs->kvm_run->psw_addr = env->psw.addr;
      cs->kvm_run->psw_mask = env->psw.mask;
- if (can_sync_regs(cs, KVM_SYNC_GPRS)) { 
-        for (i = 0; i < 16; i++) {
-            cs->kvm_run->s.regs.gprs[i] = env->regs[i];
-            cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_GPRS;
-        }
-    } else {
-        for (i = 0; i < 16; i++) {
-            regs.gprs[i] = env->regs[i];
-        }
-        r = kvm_vcpu_ioctl(cs, KVM_SET_REGS, &regs);
-        if (r < 0) {
-            return r;
-        }
+    g_assert((cs->kvm_run->kvm_valid_regs & required_syncs) == required_syncs);
+    cs->kvm_run->kvm_dirty_regs |= required_syncs;
+    for (i = 0; i < 16; i++) {
+        cs->kvm_run->s.regs.gprs[i] = env->regs[i];
+        cs->kvm_run->s.regs.acrs[i] = env->aregs[i];
+        cs->kvm_run->s.regs.crs[i] = env->cregs[i];
      }
+ cs->kvm_run->s.regs.prefix = env->psa; 
+
      if (can_sync_regs(cs, KVM_SYNC_VRS)) {
          for (i = 0; i < 32; i++) {
              cs->kvm_run->s.regs.vrs[i][0] = env->vregs[i][0];
@@ -572,25 +573,6 @@ int kvm_arch_put_registers(CPUState *cs, int level)
          }
      }
- /* access registers and control registers*/ 
-    if (can_sync_regs(cs, KVM_SYNC_ACRS | KVM_SYNC_CRS)) {
-        for (i = 0; i < 16; i++) {
-            cs->kvm_run->s.regs.acrs[i] = env->aregs[i];
-            cs->kvm_run->s.regs.crs[i] = env->cregs[i];
-        }
-        cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_ACRS;
-        cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_CRS;
-    } else {
-        for (i = 0; i < 16; i++) {
-            sregs.acrs[i] = env->aregs[i];
-            sregs.crs[i] = env->cregs[i];
-        }
-        r = kvm_vcpu_ioctl(cs, KVM_SET_SREGS, &sregs);
-        if (r < 0) {
-            return r;
-        }
-    }
-
      if (can_sync_regs(cs, KVM_SYNC_GSCB)) {
          memcpy(cs->kvm_run->s.regs.gscb, env->gscb, 32);
          cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_GSCB;
@@ -612,22 +594,15 @@ int kvm_arch_put_registers(CPUState *cs, int level)
          cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_DIAG318;
      }
- /* Finally the prefix */ 
-    if (can_sync_regs(cs, KVM_SYNC_PREFIX)) {
-        cs->kvm_run->s.regs.prefix = env->psa;
-        cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_PREFIX;
-    } else {
-        /* prefix is only supported via sync regs */
-    }
      return 0;
  }
int kvm_arch_get_registers(CPUState *cs) 
  {
+    const int required_syncs = KVM_SYNC_GPRS | KVM_SYNC_ACRS |
+                               KVM_SYNC_CRS | KVM_SYNC_PREFIX;
      S390CPU *cpu = S390_CPU(cs);
      CPUS390XState *env = &cpu->env;
-    struct kvm_sregs sregs;
-    struct kvm_regs regs;
      struct kvm_fpu fpu;
      int i, r;
@@ -635,37 +610,16 @@ int kvm_arch_get_registers(CPUState *cs) 
      env->psw.addr = cs->kvm_run->psw_addr;
      env->psw.mask = cs->kvm_run->psw_mask;
- /* the GPRS */ 
-    if (can_sync_regs(cs, KVM_SYNC_GPRS)) {
-        for (i = 0; i < 16; i++) {
-            env->regs[i] = cs->kvm_run->s.regs.gprs[i];
-        }
-    } else {
-        r = kvm_vcpu_ioctl(cs, KVM_GET_REGS, &regs);
-        if (r < 0) {
-            return r;
-        }
-         for (i = 0; i < 16; i++) {
-            env->regs[i] = regs.gprs[i];
-        }
+    /* the GPRS, ACRS and CRS */
+    g_assert((cs->kvm_run->kvm_valid_regs & required_syncs) == required_syncs);
+    for (i = 0; i < 16; i++) {
+        env->regs[i] = cs->kvm_run->s.regs.gprs[i];
+        env->aregs[i] = cs->kvm_run->s.regs.acrs[i];
+        env->cregs[i] = cs->kvm_run->s.regs.crs[i];
      }
- /* The ACRS and CRS */ 
-    if (can_sync_regs(cs, KVM_SYNC_ACRS | KVM_SYNC_CRS)) {
-        for (i = 0; i < 16; i++) {
-            env->aregs[i] = cs->kvm_run->s.regs.acrs[i];
-            env->cregs[i] = cs->kvm_run->s.regs.crs[i];
-        }
-    } else {
-        r = kvm_vcpu_ioctl(cs, KVM_GET_SREGS, &sregs);
-        if (r < 0) {
-            return r;
-        }
-         for (i = 0; i < 16; i++) {
-            env->aregs[i] = sregs.acrs[i];
-            env->cregs[i] = sregs.crs[i];
-        }
-    }
+    /* The prefix */
+    env->psa = cs->kvm_run->s.regs.prefix;
/* Floating point and vector registers */ 
      if (can_sync_regs(cs, KVM_SYNC_VRS)) {
@@ -690,11 +644,6 @@ int kvm_arch_get_registers(CPUState *cs)
          env->fpc = fpu.fpc;
      }
- /* The prefix */ 
-    if (can_sync_regs(cs, KVM_SYNC_PREFIX)) {
-        env->psa = cs->kvm_run->s.regs.prefix;
-    }
-
      if (can_sync_regs(cs, KVM_SYNC_ARCH0)) {
          env->cputm = cs->kvm_run->s.regs.cputm;
          env->ckc = cs->kvm_run->s.regs.ckc;
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