Re: [Qemu-devel] [PATCH v2 4/4] spapr: Introduce FWNMI KVM capability

[Thomas Huth <thuth@redhat.com>]

On 16/12/15 07:08, Aravinda Prasad wrote:
> Introduce a new KVM capability to control how KVM
> behaves on machine check exception.
> 
> Without this capability, KVM redirects machine check
> exceptions to guest's 0x200 vector if the address in
> error belongs to guest. With this capability KVM
> causes a guest exit with NMI exit reason.
> 
> This is required to avoid problem if a new kernel/KVM
> is used with an old QEMU. As old QEMU might not
> understand the new NMI exit type and treat it as a
> fatal error, even though the guest could have actually
> handled the error if the exception was delivered to
> guest's 0x200 interrupt vector.
> 
> PS: KVM_CAP_PPC_FWNMI is set to 121 as 119 and 120 are
> used by KVM_CAP_GUEST_DEBUG_HW_BPS and KVM_CAP_GUEST_DEBUG_HW_WPS
> in KVM code, but still not reflected in QEMU code.
> 
> Signed-off-by: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
> ---
>  hw/ppc/spapr_rtas.c       |   17 +++++++++++++++++
>  linux-headers/linux/kvm.h |    1 +
>  target-ppc/kvm.c          |    2 ++
>  3 files changed, 20 insertions(+)
> 
> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> index 17c4672..53319da 100644
> --- a/hw/ppc/spapr_rtas.c
> +++ b/hw/ppc/spapr_rtas.c
> @@ -38,6 +38,8 @@
>  #include <libfdt.h>
>  #include "hw/ppc/spapr_drc.h"
>  
> +extern int cap_fwnmi;
> +
>  /* #define DEBUG_SPAPR */
>  
>  #ifdef DEBUG_SPAPR
> @@ -603,9 +605,24 @@ static void rtas_ibm_nmi_register(PowerPCCPU *cpu,
>                                    target_ulong args,
>                                    uint32_t nret, target_ulong rets)
>  {
> +    int ret;
> +    CPUState *cs = CPU(cpu);
> +
> +    if (!cap_fwnmi) {
> +        rtas_st(rets, 0, RTAS_OUT_NOT_SUPPORTED);
> +        return;
> +    }
> +
>      spapr->mc_in_progress = false;
>      qemu_cond_init(&spapr->mc_delivery_cond);
>      spapr->guest_machine_check_addr = rtas_ld(args, 1);
> +
> +    ret = kvm_vcpu_enable_cap(cs, KVM_CAP_PPC_FWNMI, 0);
> +    if (ret < 0) {
> +        rtas_st(rets, 0, RTAS_OUT_HW_ERROR);
> +        return;
> +    }
> +
>      rtas_st(rets, 0, RTAS_OUT_SUCCESS);
>  }
>  
> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
> index 683f713..2db1fba 100644
> --- a/linux-headers/linux/kvm.h
> +++ b/linux-headers/linux/kvm.h
> @@ -819,6 +819,7 @@ struct kvm_ppc_smmu_info {
>  #define KVM_CAP_DISABLE_QUIRKS 116
>  #define KVM_CAP_X86_SMM 117
>  #define KVM_CAP_MULTI_ADDRESS_SPACE 118
> +#define KVM_CAP_PPC_FWNMI 121
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  

As far as I know, the proper way to update the files in the
linux-headers directory, is to use the scripts/update-linux-headers.sh
script to refresh them. So you also have to make sure that the line with
KVM_CAP_PPC_FWNMI has been accepted first by the upstream kernel folks,
i.e. it should be first in Paolo's KVM tree for example before you can
update the QEMU sources.

Please also do that update in a separate patch (since it can get bigger
sometimes; and that way it can also be ACKed separately from people who
are not directly involved in the ppc stuff).

 Thomas