[PATCH] qemu-kvm: Add KVM_CAP_X86_ROBUST_SINGLESTEP-awareness

[Jan Kiszka <jan.kiszka@siemens.com>]

This add-on patch to recent guest debugging refactorings adds the
requested awareness for KVM_CAP_X86_ROBUST_SINGLESTEP to both the
upstream as well as qemu-kvm's own code. Fortunately, code sharing
increased once again.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

Note: Due to missing VCPU events synchronization during runtime in
qemu-kvm, exception re-injection is unfortunately now broken (I missed a
circular dependency in my series). However, the remaining VCPU state
refactoring bits will be posted soon, and they will fix it again.
Upstream code is not affected.

 kvm-all.c         |   12 +++++++++++
 kvm.h             |    1 +
 qemu-kvm-x86.c    |   27 ++----------------------
 qemu-kvm.h        |    1 +
 target-i386/kvm.c |   60 +++++++++++++++++++++++++++++++----------------------
 5 files changed, 51 insertions(+), 50 deletions(-)

diff --git a/kvm-all.c b/kvm-all.c
index bed562f..0776bf5 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -65,6 +65,7 @@ struct KVMState
     int broken_set_mem_region;
     int migration_log;
     int vcpu_events;
+    int robust_singlestep;
 #ifdef KVM_CAP_SET_GUEST_DEBUG
     struct kvm_sw_breakpoint_head kvm_sw_breakpoints;
 #endif
@@ -673,6 +674,12 @@ int kvm_init(int smp_cpus)
     s->vcpu_events = kvm_check_extension(s, KVM_CAP_VCPU_EVENTS);
 #endif
 
+    s->robust_singlestep = 0;
+#ifdef KVM_CAP_X86_ROBUST_SINGLESTEP
+    s->robust_singlestep =
+        kvm_check_extension(s, KVM_CAP_X86_ROBUST_SINGLESTEP);
+#endif
+
     ret = kvm_arch_init(s, smp_cpus);
     if (ret < 0)
         goto err;
@@ -932,6 +939,11 @@ int kvm_has_vcpu_events(void)
     return kvm_state->vcpu_events;
 }
 
+int kvm_has_robust_singlestep(void)
+{
+    return kvm_state->robust_singlestep;
+}
+
 void kvm_setup_guest_memory(void *start, size_t size)
 {
     if (!kvm_has_sync_mmu()) {
diff --git a/kvm.h b/kvm.h
index a78a27f..427dad0 100644
--- a/kvm.h
+++ b/kvm.h
@@ -43,6 +43,7 @@ int kvm_log_stop(target_phys_addr_t phys_addr, ram_addr_t size);
 
 int kvm_has_sync_mmu(void);
 int kvm_has_vcpu_events(void);
+int kvm_has_robust_singlestep(void);
 int kvm_put_vcpu_events(CPUState *env);
 int kvm_get_vcpu_events(CPUState *env);
 
diff --git a/qemu-kvm-x86.c b/qemu-kvm-x86.c
index 5af9ce1..5db95f8 100644
--- a/qemu-kvm-x86.c
+++ b/qemu-kvm-x86.c
@@ -922,31 +922,8 @@ void kvm_arch_load_regs(CPUState *env)
     if (rc == -1)
         perror("kvm_set_msrs FAILED");
 
-    /*
-     * Kernels before 2.6.33 (which correlates with !kvm_has_vcpu_events())
-     * overwrote flags.TF injected via SET_GUEST_DEBUG while updating GP regs.
-     * Work around this by updating the debug state once again if
-     * single-stepping is on.
-     * Another reason to call kvm_update_guest_debug here is a pending debug
-     * trap raise by the guest. On kernels without SET_VCPU_EVENTS we have to
-     * reinject them via SET_GUEST_DEBUG.
-     */
-    if (!kvm_has_vcpu_events() &&
-        (env->exception_injected != -1 || env->singlestep_enabled)) {
-        unsigned long reinject_trap = 0;
-
-        if (env->exception_injected == 1) {
-            reinject_trap = KVM_GUESTDBG_INJECT_DB;
-        } else if (env->exception_injected == 3) {
-            reinject_trap = KVM_GUESTDBG_INJECT_BP;
-        }
-        env->exception_injected = -1;
-
-        rc = kvm_update_guest_debug(env, reinject_trap);
-        if (rc < 0) {
-            perror("kvm_update_guest_debug FAILED");
-        }
-    }
+    /* must be last */
+    kvm_guest_debug_workarounds(env);
 }
 
 void kvm_load_tsc(CPUState *env)
diff --git a/qemu-kvm.h b/qemu-kvm.h
index 93b144f..172eba8 100644
--- a/qemu-kvm.h
+++ b/qemu-kvm.h
@@ -1027,6 +1027,7 @@ struct KVMState {
     int broken_set_mem_region;
     int migration_log;
     int vcpu_events;
+    int robust_singlestep;
 #ifdef KVM_CAP_SET_GUEST_DEBUG
     QTAILQ_HEAD(, kvm_sw_breakpoint) kvm_sw_breakpoints;
 #endif
diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 01963e1..cf64c9a 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -853,6 +853,37 @@ int kvm_get_vcpu_events(CPUState *env)
     return 0;
 }
 
+static int kvm_guest_debug_workarounds(CPUState *env)
+{
+    int ret = 0;
+#ifdef KVM_CAP_SET_GUEST_DEBUG
+    unsigned long reinject_trap = 0;
+
+    if (!kvm_has_vcpu_events()) {
+        if (env->exception_injected == 1) {
+            reinject_trap = KVM_GUESTDBG_INJECT_DB;
+        } else if (env->exception_injected == 3) {
+            reinject_trap = KVM_GUESTDBG_INJECT_BP;
+        }
+        env->exception_injected = -1;
+    }
+
+    /*
+     * Kernels before KVM_CAP_X86_ROBUST_SINGLESTEP overwrote flags.TF
+     * injected via SET_GUEST_DEBUG while updating GP regs. Work around this
+     * by updating the debug state once again if single-stepping is on.
+     * Another reason to call kvm_update_guest_debug here is a pending debug
+     * trap raise by the guest. On kernels without SET_VCPU_EVENTS we have to
+     * reinject them via SET_GUEST_DEBUG.
+     */
+    if (reinject_trap ||
+        (!kvm_has_robust_singlestep() && env->singlestep_enabled)) {
+        ret = kvm_update_guest_debug(env, reinject_trap);
+    }
+#endif /* KVM_CAP_SET_GUEST_DEBUG */
+    return ret;
+}
+
 #ifdef KVM_UPSTREAM
 int kvm_arch_put_registers(CPUState *env)
 {
@@ -882,31 +913,10 @@ int kvm_arch_put_registers(CPUState *env)
     if (ret < 0)
         return ret;
 
-    /*
-     * Kernels before 2.6.33 (which correlates with !kvm_has_vcpu_events())
-     * overwrote flags.TF injected via SET_GUEST_DEBUG while updating GP regs.
-     * Work around this by updating the debug state once again if
-     * single-stepping is on.
-     * Another reason to call kvm_update_guest_debug here is a pending debug
-     * trap raise by the guest. On kernels without SET_VCPU_EVENTS we have to
-     * reinject them via SET_GUEST_DEBUG.
-     */
-    if (!kvm_has_vcpu_events() &&
-        (env->exception_injected != -1 || env->singlestep_enabled)) {
-        unsigned long reinject_trap = 0;
-
-        if (env->exception_injected == 1) {
-            reinject_trap = KVM_GUESTDBG_INJECT_DB;
-        } else if (env->exception_injected == 3) {
-            reinject_trap = KVM_GUESTDBG_INJECT_BP;
-        }
-        env->exception_injected = -1;
-
-        ret = kvm_update_guest_debug(env, reinject_trap);
-        if (ret < 0) {
-            return ret;
-        }
-    }
+    /* must be last */
+    ret = kvm_guest_debug_workarounds(env);
+    if (ret < 0)
+        return ret;
 
     return 0;
 }