Amit Machhiwal <[email protected]> writes:
> Currently, when booting a compatibility-mode KVM guest (L1) on a PowerNV
> hypervisor (L0), the guest runs with the expected processor
> compatibility level. However, when booting a nested KVM guest (L2)
> inside the L1, QEMU derives the CPU model from the raw host PVR and
> attempts to run the nested guest at that level, instead of honoring the
> compatibility mode of the L1.
>
> Extend host CPU compatibility capability reporting to support nested
> virtualization on PowerNV systems (PAPR nested API v1).
>
> For nested API v2 (PowerVM), compatibility capabilities are served from
> the cached nested_capabilities value (populated at module init via
> kvmhv_nested_init() using the H_GUEST_GET_CAPABILITIES hcall). This
> information is not available on PowerNV systems.
>
> For nested API v1, derive the compatibility capabilities from the L1
> guest by reading the "cpu-version" property from the device tree, which
> reflects the effective (logical) processor compatibility level. Map this
> value to the corresponding compatibility capability bitmap using
> KVM-specific constants.
>
> The mapping is cumulative: a system running at a given compatibility
> level is assumed to also support older generations down the supported
> chain. Note that unlike KVM on PowerVM (nested API v2), KVM on PowerNV
> currently does not strictly enforce older generation compatibility modes
> for nested guests - the reported capabilities reflect what the host CPU
> can present, not what the hypervisor independently validates.
>
> Introduce a helper kvmppc_map_compat_capabilities() to translate CPU
> version values into KVM_PPC_COMPAT_CAP bits using a fallthrough switch,
> and integrate it into kvmppc_get_compat_caps(). The implementation
> applies masking to ensure only supported processor modes are exposed.
>
> This allows userspace to query host CPU compatibility modes on both
> KVM on PowerVM and on PowerNV platforms via the KVM_PPC_GET_COMPAT_CAPS
> ioctl.
>
> Suggested-by: Vaibhav Jain <[email protected]>
> Tested-by: Gautam Menghani <[email protected]>
> Reviewed-by: Gautam Menghani <[email protected]>
> Tested-by: Anushree Mathur <[email protected]>
> Signed-off-by: Amit Machhiwal <[email protected]>
> ---
> arch/powerpc/kvm/book3s_hv.c | 36 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 36 insertions(+)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 152cd08a5b38..4d0307f55e06 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -6523,20 +6523,56 @@ static bool kvmppc_hash_v3_possible(void)
> return true;
> }
>
> +static int kvmppc_map_compat_capabilities(u32 cpu_version,
> + unsigned long *capabilities)
> +{
> + switch (cpu_version) {
> + case PVR_ARCH_31_P11:
> + *capabilities |= KVM_PPC_COMPAT_CAP_POWER11;
> + fallthrough;
> + case PVR_ARCH_31:
> + *capabilities |= KVM_PPC_COMPAT_CAP_POWER10;
> + fallthrough;
> + case PVR_ARCH_300:
> + *capabilities |= KVM_PPC_COMPAT_CAP_POWER9;
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> + return 0;
> +}
>
> static int kvmppc_get_compat_caps(struct kvm_ppc_compat_caps *host_caps)
> {
> + struct device_node *np;
> unsigned long capabilities = 0;
> long rc = -EINVAL;
> + u32 cpu_version = 0;
>
> if (kvmhv_on_pseries()) {
> if (kvmhv_is_nestedv2()) {
> WARN_ON_ONCE(!nested_capabilities);
> capabilities = nested_capabilities;
> rc = 0;
> + } else {
> + for_each_node_by_type(np, "cpu") {
> + if (!of_property_read_u32(np, "cpu-version",
> + &cpu_version)) {
> + of_node_put(np);
> + break;
> + }
> + }
What happens when we don't have "cpu-version" DT property?
Check this commit
5a61ef74f269f2 ("powerpc/64s: Support new device tree binding for discovering
CPU features")
And also why do we need to parse the DT properties again?
Shouldn't we check something like this?
if (cpu_has_feature(CPU_FTR_P11_PVR))
capabilities |= KVM_PPC_COMPAT_CAP_POWER11;
if (cpu_has_feature(CPU_FTR_ARCH_31))
capabilities |= KVM_PPC_COMPAT_CAP_POWER10;
if (cpu_has_feature(CPU_FTR_ARCH_300))
capabilities |= KVM_PPC_COMPAT_CAP_POWER9;
-ritesh
> + if (!cpu_version)
> + return -EINVAL;
> + rc = kvmppc_map_compat_capabilities(cpu_version,
> + &capabilities);
> }
> }
>
> + if (rc < 0)
> + return rc;
> +
> host_caps->compat_capabilities = capabilities & KVM_PPC_COMPAT_BITMASK;
>
> return rc;
> --
> 2.50.1 (Apple Git-155)
