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

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

Cc'ing qemu-ppc@

On Mon, 28 Sep 2015 12:13:47 +0200
Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:
> 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 <gkurz@linux.vnet.ibm.com>
> ---
>  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;
> 
>