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Mon, 08 Jun 2026 20:10:15 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay06.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 658KABlg16187670 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 8 Jun 2026 20:10:12 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C1C9C20040; Mon, 8 Jun 2026 20:10:11 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DE2D420043; Mon, 8 Jun 2026 20:10:07 +0000 (GMT) Received: from localhost.localdomain (unknown [9.124.208.180]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 8 Jun 2026 20:10:07 +0000 (GMT) From: Amit Machhiwal To: linuxppc-dev@lists.ozlabs.org, Madhavan Srinivasan Cc: Amit Machhiwal , Vaibhav Jain , Harsh Prateek Bora , Ritesh Harjani , Anushree Mathur , Gautam Menghani , Mukesh Kumar Chaurasiya , Nicholas Piggin , Michael Ellerman , "Christophe Leroy (CS GROUP)" , Thomas Huth , kvm@vger.kernel.org, stable@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] KVM: PPC: Book3S HV: Validate arch_compat against host compatibility mode Date: Tue, 9 Jun 2026 01:40:01 +0530 Message-ID: <20260608201001.65760-1-amachhiw@linux.ibm.com> X-Mailer: git-send-email 2.50.1 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjA4MDE4MiBTYWx0ZWRfX08rontH0jGL1 nPfxUKgiw/iAevdxbCr1/do/EcWH6mfrtHL2VCp9PIC1Jmjgbse2RlbklaygtnTObhnnidbgqwH LaK5clBfh5lLeRrSryaPnEllsxRz+BhFv/7BVigCBBuRNNCgewu+4spyoWT556B14g+iZPAbu2k 6EiD51FvFYnNteSdwzniT16loObWijbYCnMVTjYEmiAicBPNtUgCAY1mr6KZjFYWu7Vih1gzBZf rfJ3kAYYHKjFSCR/oCQzRto/GryUNLPgigCIDkE32pJ4jDConKKGXPxKUT4VunAtT/p8bP2vF1L HGmYg7AeZKGjEFoejgljD35oMftiANuW8jhmRCiwAo/XoM/nNB/41QtMaYwoDd9zjput3S597Is kMJCx5mgA2/Jo9xkvr0w2kmlBpcFvm9D+js968D/TpLtQxHiUWqwmzdj6k6GJUNGrOFpODRR5tE Jsk/HXUvm5s5FFHZUmA== X-Authority-Analysis: v=2.4 cv=HvFG3UTS c=1 sm=1 tr=0 ts=6a2721a8 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=9YAIjoFcglyEYsXf--YA:9 X-Proofpoint-ORIG-GUID: 6PiZMTJrvxEG9tkgHTQkZgB_dw4BjJDC X-Proofpoint-GUID: FplBwTkmv2YHom8WSz4ZVI5no8F0Htj7 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-08_05,2026-06-05_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1015 lowpriorityscore=0 adultscore=0 suspectscore=0 spamscore=0 priorityscore=1501 phishscore=0 malwarescore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605210000 definitions=main-2606080182 On IBM POWER systems, newer processor generations can operate in compatibility modes corresponding to earlier generations. This becomes relevant for nested virtualization, where nested KVM guests may need to run with a specific processor compatibility level. Currently, when running a nested KVM guest (L2) inside a Power11 pSeries logical partition (L1) booted in Power10 compatibility mode, the guest fails to boot while setting 'arch_compat'. This happens because the CPU class is derived from the hardware PVR (via mfspr()), which reflects the physical processor generation (Power11), rather than the effective compatibility mode (Power10). As a result, userspace may request a Power11 arch_compat for the L2 guest. However, the L1 partition, running in Power10 compatibility, has only negotiated support up to Power10 with the Power Hypervisor (L0). When H_GUEST_SET_STATE is invoked with a Power11 Logical PVR, the hypervisor rejects the request, leading to a late guest boot failure: KVM-NESTEDv2: couldn't set guest wide elements [..KVM reg dump..] This situation should be detected earlier and rejected by KVM. Without proper validation, if userspace ignores the error, the guest may continue to boot in Power11 raw mode on a Power10 compatibility host, which should not be allowed. Introduce a validation mechanism that detects unsupported arch_compat values early in the guest initialization path. When an unsupported arch_compat is requested (e.g., Power11 on a Power10 compatibility mode host), kvmppc_set_arch_compat() uses cpu_has_feature(CPU_FTR_P11_PVR) to detect the mismatch and sets arch_compat to PVR_ARCH_INVALID. This triggers kvmppc_sanity_check() to mark the vCPU as invalid by setting vcpu->arch.sane to false. On the next vCPU run, kvmppc_vcpu_run_hv() checks this flag and returns -EINVAL, preventing the guest from running with an invalid processor compatibility configuration. With this, when a Power11 arch_compat is requested on a Power10 compatibility mode host, the guest fails early during boot with: error: kvm run failed Invalid argument This provides a much clearer failure mode compared to the previous behavior where the guest could boot in Power11 raw mode (if userspace ignored the error) or fail late during H_GUEST_SET_STATE. Suggested-by: Vaibhav Jain Cc: stable@vger.kernel.org # v6.13+ Signed-off-by: Amit Machhiwal --- Changes in v2: * Fixed issue where v1 allowed guest to boot in Power11 raw mode when userspace ignored the error, by adding validation in kvmppc_sanity_check() to ensure early failure during vCPU run [Found the issue after posting v1, also reported by Gautam.] * Introduced PVR_ARCH_INVALID constant for marking invalid arch_compat * Dropped all Reviewed-by and Tested-by tags due to code changes; requesting fresh reviews * v1: https://lore.kernel.org/all/20260603141539.47620-1-amachhiw@linux.ibm.com/ Changes in v1: * Moved this patch out of the v3 series [1] as discussed here [2] * Addressed below review comments from Ritesh: - Based the PVR validation on cpu features - Fixed hcall name typo - Stable backport [1] https://lore.kernel.org/all/20260522152744.55251-1-amachhiw@linux.ibm.com/ [2] https://lore.kernel.org/all/20260522152744.55251-2-amachhiw@linux.ibm.com/ --- arch/powerpc/include/asm/reg.h | 1 + arch/powerpc/kvm/book3s_hv.c | 15 ++++++++++++++- arch/powerpc/kvm/powerpc.c | 3 +++ 3 files changed, 18 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h index 3449dd2b577d..7472b9522f71 100644 --- a/arch/powerpc/include/asm/reg.h +++ b/arch/powerpc/include/asm/reg.h @@ -1356,6 +1356,7 @@ #define PVR_ARCH_300 0x0f000005 #define PVR_ARCH_31 0x0f000006 #define PVR_ARCH_31_P11 0x0f000007 +#define PVR_ARCH_INVALID 0xffffffff /* Macros for setting and retrieving special purpose registers */ #ifndef __ASSEMBLER__ diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index 61dbeea317f3..f9380ef65750 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -446,7 +446,19 @@ static int kvmppc_set_arch_compat(struct kvm_vcpu *vcpu, u32 arch_compat) guest_pcr_bit = PCR_ARCH_300; break; case PVR_ARCH_31: + guest_pcr_bit = PCR_ARCH_31; + break; case PVR_ARCH_31_P11: + /* + * Need to check this for ISA 3.1, as Power10 and + * Power11 share the same PCR. For any subsequent ISA + * versions, this will be taken care of by the guest vs + * host PCR comparison below. + */ + if (!cpu_has_feature(CPU_FTR_P11_PVR)) { + arch_compat = PVR_ARCH_INVALID; + goto out; + } guest_pcr_bit = PCR_ARCH_31; break; default: @@ -469,6 +481,7 @@ static int kvmppc_set_arch_compat(struct kvm_vcpu *vcpu, u32 arch_compat) return -EINVAL; } +out: spin_lock(&vc->lock); vc->arch_compat = arch_compat; kvmhv_nestedv2_mark_dirty(vcpu, KVMPPC_GSID_LOGICAL_PVR); @@ -479,7 +492,7 @@ static int kvmppc_set_arch_compat(struct kvm_vcpu *vcpu, u32 arch_compat) vc->pcr = (host_pcr_bit - guest_pcr_bit) | PCR_MASK; spin_unlock(&vc->lock); - return 0; + return kvmppc_sanity_check(vcpu); } static void kvmppc_dump_regs(struct kvm_vcpu *vcpu) diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c index 00302399fc37..7e2d489af642 100644 --- a/arch/powerpc/kvm/powerpc.c +++ b/arch/powerpc/kvm/powerpc.c @@ -258,6 +258,9 @@ int kvmppc_sanity_check(struct kvm_vcpu *vcpu) if (!vcpu->arch.pvr) goto out; + if (vcpu->arch.vcore->arch_compat == PVR_ARCH_INVALID) + goto out; + /* PAPR only works with book3s_64 */ if ((vcpu->arch.cpu_type != KVM_CPU_3S_64) && vcpu->arch.papr_enabled) goto out; base-commit: 4549871118cf616eecdd2d939f78e3b9e1dddc48 -- 2.50.1 (Apple Git-155)