Re: [PATCH] powerpc/dt_cpu_ftrs: Set CPU_FTR_P11_PVR for Power11 and later processors

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

Le 14/06/2026 à 19:34, Amit Machhiwal a écrit :
> 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: stable@vger.kernel.org # v6.13+
> Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>
> ---
> Related: https://lore.kernel.org/all/20260609053327.61563-1-amachhiw@linux.ibm.com/
> ---
> 
>   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)

Are we sure this test will always be correct ?

For instance PVR_PA6T is higher than PVR_POWER11 allthough it is not ISA 3.1

Wouldn't is be cleaner and safer to just do:

	PVR_VER(mfspr(SPRN_PVR)) == PVR_POWER11

> +			cur_cpu_spec->cpu_features |= CPU_FTR_P11_PVR;
>   	}
>   }
>   
> 
> base-commit: 424280953322cf66314f3ba5e2d1ef345f21c770