On Sun, Jun 14, 2026 at 11:04:37PM +0530, Amit Machhiwal wrote:
> When using device tree CPU features (dt-cpu-ftrs), the kernel bypasses
> the traditional cputable-based CPU identification and instead derives
> CPU features from the device tree's "ibm,powerpc-cpu-features" node
> provided by firmware.
>
> However, CPU_FTR_P11_PVR is a kernel-internal feature flag used to
> identify Power11 and later processors, and is not represented in the
> device tree's ISA feature set. While ISA v3.1 support (indicated by
> CPU_FTR_ARCH_31) is present on both Power10 and Power11, the
> CPU_FTR_P11_PVR flag is specifically needed by code that must
> distinguish between Power10 and Power11 processors.
>
> Without this flag set, code that checks for Power11 using
> cpu_has_feature(CPU_FTR_P11_PVR) will incorrectly return false on
> Power11+ systems using dt-cpu-ftrs, leading to incorrect behavior.
>
> This issue manifests specifically in powernv environments (bare-metal
> or QEMU TCG with powernv machine type), where skiboot/OPAL firmware
> provides the "ibm,powerpc-cpu-features" node, causing the kernel to
> use dt-cpu-ftrs. The issue does not affect pseries guests, where SLOF
> firmware does not provide this node, causing the kernel to fall back
> to the traditional cputable path (identify_cpu) which correctly sets
> CPU_FTR_P11_PVR during PVR-based CPU identification.
>
> In powernv TCG guests, the missing flag causes KVM code to trigger
> warnings when attempting to create KVM guests, as cpu_features shows
> 0x000c00eb8f4fb187 (missing bit 53) instead of the correct
> 0x002c00eb8f4fb187 (with bit 53 set).
>
> Fix this by setting CPU_FTR_P11_PVR for all processors with
> PVR >= PVR_POWER11 when ISA v3.1 support is detected in
> cpufeatures_setup_start(). This approach ensures forward
> compatibility with future processor generations.
>
> Fixes: 96e266e3bcd6 ("KVM: PPC: Book3S HV: Add Power11 capability support for
> Nested PAPR guests")
> Cc: [email protected] # v6.13+
> Signed-off-by: Amit Machhiwal <[email protected]>
> ---
> Related:
> https://lore.kernel.org/all/[email protected]/
> ---
>
> arch/powerpc/kernel/dt_cpu_ftrs.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c
> b/arch/powerpc/kernel/dt_cpu_ftrs.c
> index 3af6c06af02f..e5853daa6a48 100644
> --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
> +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
> @@ -704,6 +704,15 @@ static void __init cpufeatures_setup_start(u32 isa)
> if (isa >= ISA_V3_1) {
> cur_cpu_spec->cpu_features |= CPU_FTR_ARCH_31;
> cur_cpu_spec->cpu_user_features2 |= PPC_FEATURE2_ARCH_3_1;
> +
> + /*
> + * CPU_FTR_P11_PVR is a kernel-internal flag to identify
> + * Power11 and later processors. While ISA v3.1 is supported
> + * by Power10+, this flag specifically indicates Power11+
> + * for code that needs to distinguish between P10 and P11.
> + */
> + if (PVR_VER(mfspr(SPRN_PVR)) >= PVR_POWER11)
> + cur_cpu_spec->cpu_features |= CPU_FTR_P11_PVR;
> }
> }
>
>
> base-commit: 424280953322cf66314f3ba5e2d1ef345f21c770
> --
> 2.50.1 (Apple Git-155)
>
LGTM
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]>
