[Qemu-devel] [PATCH] spapr: add a default rng device

[Greg Kurz]

A recent patch by Thomas Huth brought a new spapr-rng pseudo-device to
provide high-quality random numbers to guests. The device may either be
backed by a "RngBackend" or the in-kernel implementation of the H_RANDOM
hypercall.

Since modern POWER8 based servers always provide a hardware rng, it makes
sense to create a spapr-rng device with use-kvm=true by default when it
is available.

Of course we want the user to have full control on how the rng is handled.
The default device WILL NOT be created in the following cases:
- the -nodefaults option was passed
- a spapr-rng device was already passed on the command line

The default device is created at reset time to ensure devices specified on
the command line have been created.

Signed-off-by: Greg Kurz <address@hidden>
---
 hw/ppc/spapr.c       |   17 +++++++++++++++++
 hw/ppc/spapr_rng.c   |    2 +-
 target-ppc/kvm.c     |    9 +++++----
 target-ppc/kvm_ppc.h |    6 ++++++
 4 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 7f4f196e53e5..ee048ecffd0c 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1059,6 +1059,14 @@ static int spapr_check_htab_fd(sPAPRMachineState *spapr)
     return rc;
 }
 
+static void spapr_rng_create(void)
+{
+    Object *rng = object_new(TYPE_SPAPR_RNG);
+
+    object_property_set_bool(rng, true, "use-kvm", &error_abort);
+    object_property_set_bool(rng, true, "realized", &error_abort);
+}
+
 static void ppc_spapr_reset(void)
 {
     sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
@@ -1082,6 +1090,15 @@ static void ppc_spapr_reset(void)
     spapr->rtas_addr = rtas_limit - RTAS_MAX_SIZE;
     spapr->fdt_addr = spapr->rtas_addr - FDT_MAX_SIZE;
 
+    /* Create a rng device if the user did not provide it already and
+     * KVM has hwrng support.
+     */
+    if (defaults_enabled() &&
+        kvmppc_hwrng_present() &&
+        !object_resolve_path_type("", TYPE_SPAPR_RNG, NULL)) {
+        spapr_rng_create();
+    }
+
     /* Load the fdt */
     spapr_finalize_fdt(spapr, spapr->fdt_addr, spapr->rtas_addr,
                        spapr->rtas_size);
diff --git a/hw/ppc/spapr_rng.c b/hw/ppc/spapr_rng.c
index ed43d5e04221..ee5af302bd4d 100644
--- a/hw/ppc/spapr_rng.c
+++ b/hw/ppc/spapr_rng.c
@@ -114,7 +114,7 @@ static void spapr_rng_realize(DeviceState *dev, Error 
**errp)
     sPAPRRngState *rngstate = SPAPR_RNG(dev);
 
     if (rngstate->use_kvm) {
-        if (kvmppc_enable_hwrng() == 0) {
+        if (kvmppc_hwrng_present() && kvmppc_enable_hwrng() == 0) {
             return;
         }
         /*
diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
index e641680fb146..084bb034f1fd 100644
--- a/target-ppc/kvm.c
+++ b/target-ppc/kvm.c
@@ -2490,11 +2490,12 @@ int kvm_arch_msi_data_to_gsi(uint32_t data)
     return data & 0xffff;
 }
 
-int kvmppc_enable_hwrng(void)
+bool kvmppc_hwrng_present(void)
 {
-    if (!kvm_enabled() || !kvm_check_extension(kvm_state, KVM_CAP_PPC_HWRNG)) {
-        return -1;
-    }
+    return kvm_enabled() && kvm_check_extension(kvm_state, KVM_CAP_PPC_HWRNG);
+}
 
+int kvmppc_enable_hwrng(void)
+{
     return kvmppc_enable_hcall(kvm_state, H_RANDOM);
 }
diff --git a/target-ppc/kvm_ppc.h b/target-ppc/kvm_ppc.h
index 470f6d62f7bb..a76338c9aa16 100644
--- a/target-ppc/kvm_ppc.h
+++ b/target-ppc/kvm_ppc.h
@@ -54,6 +54,7 @@ void kvmppc_hash64_free_pteg(uint64_t token);
 void kvmppc_hash64_write_pte(CPUPPCState *env, target_ulong pte_index,
                              target_ulong pte0, target_ulong pte1);
 bool kvmppc_has_cap_fixup_hcalls(void);
+bool kvmppc_hwrng_present(void);
 int kvmppc_enable_hwrng(void);
 
 #else
@@ -252,6 +253,11 @@ static inline bool kvmppc_has_cap_fixup_hcalls(void)
     abort();
 }
 
+static inline bool kvmppc_hwrng_present(void)
+{
+    return false;
+}
+
 static inline int kvmppc_enable_hwrng(void)
 {
     return -1;