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 <redacted>
---
Related: https://lore.kernel.org/all/20260609053327.61563-1-amachhiw@linux.ibm.com/ (local)
---

 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)