Messages in this thread Patch in this message |  | | Date | Tue, 5 May 2026 14:01:44 +0530 | | Subject | Re: [PATCH 2/6] KVM: PPC: Introduce KVM_CAP_PPC_COMPAT_CAPS and KVM_PPC_GET_COMPAT_CAPS | | From | Harsh Prateek Bora <> |
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On 30/04/26 11:19 am, Amit Machhiwal wrote: > Introduce a new capability and ioctl to expose CPU compatibility modes > supported by the host processor for nested guests. > > Introduce a new KVM capability, KVM_CAP_PPC_COMPAT_CAPS, and a > corresponding vm ioctl, KVM_PPC_GET_COMPAT_CAPS, to expose processor > compatibility modes supported by the host. > > On IBM POWER systems, newer processor generations (N) can operate in > compatibility modes corresponding to earlier generations, like (N-1) and > (N-2). This is particularly relevant for nested virtualization, where > nested KVM guests may need to run with a specific processor compatibility > level. > > The new ioctl returns a bitmap describing the compatibility modes > supported by the host in respective bit numbers. This allows userspace > to select an appropriate compatibility level when configuring nested KVM > guests. > > Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com> > --- > arch/powerpc/include/uapi/asm/kvm.h | 6 ++++++ > include/uapi/linux/kvm.h | 4 ++++ > 2 files changed, 10 insertions(+) > > diff --git a/arch/powerpc/include/uapi/asm/kvm.h b/arch/powerpc/include/uapi/asm/kvm.h > index 077c5437f521..a38dff7a8aea 100644 > --- a/arch/powerpc/include/uapi/asm/kvm.h > +++ b/arch/powerpc/include/uapi/asm/kvm.h > @@ -437,6 +437,12 @@ struct kvm_ppc_cpu_char { > __u64 behaviour_mask; /* valid bits in behaviour */ > }; > > +/* For KVM_PPC_GET_COMPAT_CAPS */ > +struct kvm_ppc_compat_caps { > + __u32 flags;
You may either want flags to be __u64, or rearrange to keep variables in descending order of size or add padding as appropriate. Also, if we are not using flags with this series, we need to document comment as /* reserved for future use */
> + __u64 compat_capabilities; /* Capabilities supported by the host */ > +}; > + > /* > * Values for character and character_mask. > * These are identical to the values used by H_GET_CPU_CHARACTERISTICS. > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index 6c8afa2047bf..1788a0068662 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -996,6 +996,7 @@ struct kvm_enable_cap { > #define KVM_CAP_S390_USER_OPEREXEC 246 > #define KVM_CAP_S390_KEYOP 247 > #define KVM_CAP_S390_VSIE_ESAMODE 248 > +#define KVM_CAP_PPC_COMPAT_CAPS 249 > > struct kvm_irq_routing_irqchip { > __u32 irqchip; > @@ -1349,6 +1350,9 @@ struct kvm_s390_keyop { > #define KVM_GET_DEVICE_ATTR _IOW(KVMIO, 0xe2, struct kvm_device_attr) > #define KVM_HAS_DEVICE_ATTR _IOW(KVMIO, 0xe3, struct kvm_device_attr) > > +/* Available with KVM_CAP_PPC_COMPAT_CAPS */ > +#define KVM_PPC_GET_COMPAT_CAPS _IOR(KVMIO, 0xe4, struct kvm_ppc_compat_caps) > +
This patch can actually be squashed with next patch where the struct, macros are actually being used.
> /* > * ioctls for vcpu fds > */
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