[PATCH v2] target/arm: Check supported KVM features globally (not per vCPU)

[Philippe Mathieu-Daudé]

Since commit d70c996df23f, when enabling the PMU we get:

  $ qemu-system-aarch64 -cpu host,pmu=on -M virt,accel=kvm,gic-version=3
  Segmentation fault (core dumped)

  Thread 1 "qemu-system-aar" received signal SIGSEGV, Segmentation fault.
  0x0000aaaaaae356d0 in kvm_ioctl (s=0x0, type=44547) at 
accel/kvm/kvm-all.c:2588
  2588        ret = ioctl(s->fd, type, arg);
  (gdb) bt
  #0  0x0000aaaaaae356d0 in kvm_ioctl (s=0x0, type=44547) at 
accel/kvm/kvm-all.c:2588
  #1  0x0000aaaaaae31568 in kvm_check_extension (s=0x0, extension=126) at 
accel/kvm/kvm-all.c:916
  #2  0x0000aaaaaafce254 in kvm_arm_pmu_supported (cpu=0xaaaaac214ab0) at 
target/arm/kvm.c:213
  #3  0x0000aaaaaafc0f94 in arm_set_pmu (obj=0xaaaaac214ab0, value=true, 
errp=0xffffffffe438) at target/arm/cpu.c:1111
  #4  0x0000aaaaab5533ac in property_set_bool (obj=0xaaaaac214ab0, 
v=0xaaaaac223a80, name=0xaaaaac11a970 "pmu", opaque=0xaaaaac222730, 
errp=0xffffffffe438) at qom/object.c:2170
  #5  0x0000aaaaab5512f0 in object_property_set (obj=0xaaaaac214ab0, 
v=0xaaaaac223a80, name=0xaaaaac11a970 "pmu", errp=0xffffffffe438) at 
qom/object.c:1328
  #6  0x0000aaaaab551e10 in object_property_parse (obj=0xaaaaac214ab0, 
string=0xaaaaac11b4c0 "on", name=0xaaaaac11a970 "pmu", errp=0xffffffffe438) at 
qom/object.c:1561
  #7  0x0000aaaaab54ee8c in object_apply_global_props (obj=0xaaaaac214ab0, 
props=0xaaaaac018e20, errp=0xaaaaabd6fd88 <error_fatal>) at qom/object.c:407
  #8  0x0000aaaaab1dd5a4 in qdev_prop_set_globals (dev=0xaaaaac214ab0) at 
hw/core/qdev-properties.c:1218
  #9  0x0000aaaaab1d9fac in device_post_init (obj=0xaaaaac214ab0) at 
hw/core/qdev.c:1050
  ...
  #15 0x0000aaaaab54f310 in object_initialize_with_type (obj=0xaaaaac214ab0, 
size=52208, type=0xaaaaabe237f0) at qom/object.c:512
  #16 0x0000aaaaab54fa24 in object_new_with_type (type=0xaaaaabe237f0) at 
qom/object.c:687
  #17 0x0000aaaaab54fa80 in object_new (typename=0xaaaaabe23970 "host-arm-cpu") 
at qom/object.c:702
  #18 0x0000aaaaaaf04a74 in machvirt_init (machine=0xaaaaac0a8550) at 
hw/arm/virt.c:1770
  #19 0x0000aaaaab1e8720 in machine_run_board_init (machine=0xaaaaac0a8550) at 
hw/core/machine.c:1138
  #20 0x0000aaaaaaf95394 in qemu_init (argc=5, argv=0xffffffffea58, 
envp=0xffffffffea88) at softmmu/vl.c:4348
  #21 0x0000aaaaaada3f74 in main (argc=<optimized out>, argv=<optimized out>, 
envp=<optimized out>) at softmmu/main.c:48

This is because in frame #2, cpu->kvm_state is still NULL
(the vCPU is not yet realized).

KVM has a hard requirement of all cores supporting the same
feature set. We only need to check if the accelerator supports
a feature, not each vCPU individually.

Fix by kvm_arm_<FEATURE>_supported() functions take a AccelState
argument (already realized/valid at this point) instead of a
CPUState argument.

Reported-by: Haibo Xu <haibo.xu@linaro.org>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
v2: Use global kvm_state (bonzini)

Paolo, does this break migration of encrypted memory assumptions?

Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Supersedes: <20200617130800.26355-1-philmd@redhat.com>
---
 target/arm/kvm_arm.h | 21 +++++++++------------
 target/arm/cpu.c     |  2 +-
 target/arm/cpu64.c   | 10 +++++-----
 target/arm/kvm.c     |  4 ++--
 target/arm/kvm64.c   | 14 +++++---------
 5 files changed, 22 insertions(+), 29 deletions(-)

diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
index 48bf5e16d5..a4ce4fd93d 100644
--- a/target/arm/kvm_arm.h
+++ b/target/arm/kvm_arm.h
@@ -269,29 +269,26 @@ void kvm_arm_add_vcpu_properties(Object *obj);
 
 /**
  * kvm_arm_aarch32_supported:
- * @cs: CPUState
  *
- * Returns: true if the KVM VCPU can enable AArch32 mode
+ * Returns: true if KVM can enable AArch32 mode
  * and false otherwise.
  */
-bool kvm_arm_aarch32_supported(CPUState *cs);
+bool kvm_arm_aarch32_supported(void);
 
 /**
  * kvm_arm_pmu_supported:
- * @cs: CPUState
  *
- * Returns: true if the KVM VCPU can enable its PMU
+ * Returns: true if KVM can enable the PMU
  * and false otherwise.
  */
-bool kvm_arm_pmu_supported(CPUState *cs);
+bool kvm_arm_pmu_supported(void);
 
 /**
  * kvm_arm_sve_supported:
- * @cs: CPUState
  *
- * Returns true if the KVM VCPU can enable SVE and false otherwise.
+ * Returns true if KVM can enable SVE and false otherwise.
  */
-bool kvm_arm_sve_supported(CPUState *cs);
+bool kvm_arm_sve_supported(void);
 
 /**
  * kvm_arm_get_max_vm_ipa_size:
@@ -359,17 +356,17 @@ static inline void 
kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
 
 static inline void kvm_arm_add_vcpu_properties(Object *obj) {}
 
-static inline bool kvm_arm_aarch32_supported(CPUState *cs)
+static inline bool kvm_arm_aarch32_supported(void)
 {
     return false;
 }
 
-static inline bool kvm_arm_pmu_supported(CPUState *cs)
+static inline bool kvm_arm_pmu_supported(void)
 {
     return false;
 }
 
-static inline bool kvm_arm_sve_supported(CPUState *cs)
+static inline bool kvm_arm_sve_supported(void)
 {
     return false;
 }
diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 5b7a36b5d7..e44e18062c 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -1108,7 +1108,7 @@ static void arm_set_pmu(Object *obj, bool value, Error 
**errp)
     ARMCPU *cpu = ARM_CPU(obj);
 
     if (value) {
-        if (kvm_enabled() && !kvm_arm_pmu_supported(CPU(cpu))) {
+        if (kvm_enabled() && !kvm_arm_pmu_supported()) {
             error_setg(errp, "'pmu' feature not supported by KVM on this 
host");
             return;
         }
diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 778cecc2e6..a0c1d8894b 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -266,7 +266,7 @@ void arm_cpu_sve_finalize(ARMCPU *cpu, Error **errp)
 
     /* Collect the set of vector lengths supported by KVM. */
     bitmap_zero(kvm_supported, ARM_MAX_VQ);
-    if (kvm_enabled() && kvm_arm_sve_supported(CPU(cpu))) {
+    if (kvm_enabled() && kvm_arm_sve_supported()) {
         kvm_arm_sve_get_vls(CPU(cpu), kvm_supported);
     } else if (kvm_enabled()) {
         assert(!cpu_isar_feature(aa64_sve, cpu));
@@ -473,7 +473,7 @@ static void cpu_max_set_sve_max_vq(Object *obj, Visitor *v, 
const char *name,
         return;
     }
 
-    if (kvm_enabled() && !kvm_arm_sve_supported(CPU(cpu))) {
+    if (kvm_enabled() && !kvm_arm_sve_supported()) {
         error_setg(errp, "cannot set sve-max-vq");
         error_append_hint(errp, "SVE not supported by KVM on this host\n");
         return;
@@ -519,7 +519,7 @@ static void cpu_arm_set_sve_vq(Object *obj, Visitor *v, 
const char *name,
         return;
     }
 
-    if (value && kvm_enabled() && !kvm_arm_sve_supported(CPU(cpu))) {
+    if (value && kvm_enabled() && !kvm_arm_sve_supported()) {
         error_setg(errp, "cannot enable %s", name);
         error_append_hint(errp, "SVE not supported by KVM on this host\n");
         return;
@@ -556,7 +556,7 @@ static void cpu_arm_set_sve(Object *obj, Visitor *v, const 
char *name,
         return;
     }
 
-    if (value && kvm_enabled() && !kvm_arm_sve_supported(CPU(cpu))) {
+    if (value && kvm_enabled() && !kvm_arm_sve_supported()) {
         error_setg(errp, "'sve' feature not supported by KVM on this host");
         return;
     }
@@ -751,7 +751,7 @@ static void aarch64_cpu_set_aarch64(Object *obj, bool 
value, Error **errp)
      * uniform execution state like do_interrupt.
      */
     if (value == false) {
-        if (!kvm_enabled() || !kvm_arm_aarch32_supported(CPU(cpu))) {
+        if (!kvm_enabled() || !kvm_arm_aarch32_supported()) {
             error_setg(errp, "'aarch64' feature cannot be disabled "
                              "unless KVM is enabled and 32-bit EL1 "
                              "is supported");
diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index eef3bbd1cc..7c672c78b8 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -208,9 +208,9 @@ void kvm_arm_add_vcpu_properties(Object *obj)
     }
 }
 
-bool kvm_arm_pmu_supported(CPUState *cpu)
+bool kvm_arm_pmu_supported(void)
 {
-    return kvm_check_extension(cpu->kvm_state, KVM_CAP_ARM_PMU_V3);
+    return kvm_check_extension(kvm_state, KVM_CAP_ARM_PMU_V3);
 }
 
 int kvm_arm_get_max_vm_ipa_size(MachineState *ms)
diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
index f09ed9f4df..3dc494aaa7 100644
--- a/target/arm/kvm64.c
+++ b/target/arm/kvm64.c
@@ -652,18 +652,14 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures 
*ahcf)
     return true;
 }
 
-bool kvm_arm_aarch32_supported(CPUState *cpu)
+bool kvm_arm_aarch32_supported(void)
 {
-    KVMState *s = KVM_STATE(current_accel());
-
-    return kvm_check_extension(s, KVM_CAP_ARM_EL1_32BIT);
+    return kvm_check_extension(kvm_state, KVM_CAP_ARM_EL1_32BIT);
 }
 
-bool kvm_arm_sve_supported(CPUState *cpu)
+bool kvm_arm_sve_supported(void)
 {
-    KVMState *s = KVM_STATE(current_accel());
-
-    return kvm_check_extension(s, KVM_CAP_ARM_SVE);
+    return kvm_check_extension(kvm_state, KVM_CAP_ARM_SVE);
 }
 
 QEMU_BUILD_BUG_ON(KVM_ARM64_SVE_VQ_MIN != 1);
@@ -798,7 +794,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
         env->features &= ~(1ULL << ARM_FEATURE_PMU);
     }
     if (cpu_isar_feature(aa64_sve, cpu)) {
-        assert(kvm_arm_sve_supported(cs));
+        assert(kvm_arm_sve_supported());
         cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_SVE;
     }
 
-- 
2.21.3