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{ "id": 2232042, "url": "http://patchwork.ozlabs.org/api/covers/2232042/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-ppc/cover/20260502140021.69712-1-amachhiw@linux.ibm.com/", "project": { "id": 69, "url": "http://patchwork.ozlabs.org/api/projects/69/?format=api", "name": "QEMU powerpc development", "link_name": "qemu-ppc", "list_id": "qemu-ppc.nongnu.org", "list_email": "qemu-ppc@nongnu.org", "web_url": "", "scm_url": "", "webscm_url": "", "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20260502140021.69712-1-amachhiw@linux.ibm.com>", "list_archive_url": null, "date": "2026-05-02T14:00:18", "name": "[v2,0/3] ppc/kvm: Handle CPU compatibility mode correctly for nested guests", "submitter": { "id": 87864, "url": "http://patchwork.ozlabs.org/api/people/87864/?format=api", "name": "Amit Machhiwal", "email": "amachhiw@linux.ibm.com" }, "mbox": "http://patchwork.ozlabs.org/project/qemu-ppc/cover/20260502140021.69712-1-amachhiw@linux.ibm.com/mbox/", "series": [ { "id": 502527, "url": "http://patchwork.ozlabs.org/api/series/502527/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-ppc/list/?series=502527", "date": "2026-05-02T14:00:18", "name": "ppc/kvm: Handle CPU compatibility mode correctly for nested guests", "version": 2, "mbox": "http://patchwork.ozlabs.org/series/502527/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/covers/2232042/comments/", "headers": { "Return-Path": "<qemu-ppc-bounces+incoming=patchwork.ozlabs.org@nongnu.org>", "X-Original-To": "incoming@patchwork.ozlabs.org", "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256\n header.s=pp1 header.b=EDjx8Ed/;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc\n :content-transfer-encoding:date:from:message-id:mime-version\n :subject:to; s=pp1; bh=+KEF0RGGlu0z1YHcRdhnUWsGv9q1vdeLnOVUKCbc2\n A4=; b=EDjx8Ed/oLRMPJba62a64l9DnKtYDM3ca5Bpfo58Ap5NqV38qCy30o7aj\n vhiU8y7dNa96VEQS8RBOpAHB1JugTpFma07EMKCdRswreeC1QmV1728WS5utzLSJ\n 5yZ3ZbuT3bx1+o/s3E2xgGpmFoZiMK8+c1Xh7zLXDZRw4WvF8w09QD9nK6eUDhuJ\n HF4BN+LmW0cH9S4AvTOU3jZhmUoNoQlhCuTq7Zu+wUVfkitj3ZPG3yZhGFq1gfKm\n xeX6clp8R9ordc1Og72ynAT423pCfe+h32MsQI3rMyAIEYlbBIkxA5zbkh7bOJ5B\n 7kcVZr10xN+9N6UWqqbArpk/CgMQQ==", "From": "Amit Machhiwal <amachhiw@linux.ibm.com>", "To": "qemu-ppc@nongnu.org, Harsh Prateek Bora <harshpb@linux.ibm.com>", "Cc": "Amit Machhiwal <amachhiw@linux.ibm.com>,\n Vaibhav Jain <vaibhav@linux.ibm.com>, Nicholas Piggin <npiggin@gmail.com>,\n Chinmay Rath <rathc@linux.ibm.com>, Glenn Miles <milesg@linux.ibm.com>,\n Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org,\n kvm@vger.kernel.org", "Subject": "[PATCH v2 0/3] ppc/kvm: Handle CPU compatibility mode correctly for\n nested guests", "Date": "Sat, 2 May 2026 19:30:18 +0530", "Message-ID": "<20260502140021.69712-1-amachhiw@linux.ibm.com>", "X-Mailer": "git-send-email 2.50.1", "MIME-Version": "1.0", "Content-Transfer-Encoding": "8bit", "X-TM-AS-GCONF": "00", "X-Proofpoint-Reinject": "loops=2 maxloops=12", "X-Authority-Analysis": "v=2.4 cv=XPQAjwhE c=1 sm=1 tr=0 ts=69f6038d cx=c_pps\n a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17\n a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22\n a=Y2IxJ9c9Rs8Kov3niI8_:22 a=p0WdMEafAAAA:8 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8\n a=M_kZukdR289U2EYsLHYA:9", "X-Proofpoint-ORIG-GUID": "BhrSuD8qIEGPipBkZCAPlPXoqQ4K48C6", "X-Proofpoint-GUID": "frMv7xi41FMWDl_9MxokzL5EH7i_Rv3E", "X-Proofpoint-Spam-Details-Enc": "AW1haW4tMjYwNTAyMDEzNiBTYWx0ZWRfXzbQTG886JqAt\n TnltEK12QTxHHkBGNmlG91TyhbVpDlsJoSKfLiIxZhM9J119z38oWPs1W2cmCW0pQCYU927ylql\n dcO6LVl/pNFm+GRqb3QwBRxMBjRqVy9Ku+wCnS/hnIj1IjsLlH/i7GhyCf0B44NCqqsaFXpT+Sw\n wuS7ceRi3VfT91rQ0B2bYPrtuSfgk/N6C/UQhRVVGIxkKTAimxaXO6EA5FRYaWMi3VSRLhsActW\n OqxuRcCo0rqTjFUlXHpIvSiKwxwmzi3i+smY/h0SHp14opYIODs+WKO7sTgZHW8T0BfY71dIgUW\n djm4T0MQ6GjvFCdh5hrjqNFIs5oF+UUYXqUX17zteTPSO1+DRPeNsR5OwRkSpVa552Q2mmvgSgX\n fLLmTO8d1ZURgnwPzc7TLAV5eiBeZ8m7HTZIgerydSB3K7lGf95VlwfyNUOg55xDkyJxL+Nb8D7\n li2CXh00tVhuxpxt5oQ==", "X-Proofpoint-Virus-Version": "vendor=baseguard\n engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49\n definitions=2026-05-02_03,2026-04-30_02,2025-10-01_01", "X-Proofpoint-Spam-Details": "rule=outbound_notspam policy=outbound score=0\n bulkscore=0 lowpriorityscore=0 suspectscore=0 adultscore=0 spamscore=0\n priorityscore=1501 impostorscore=0 phishscore=0 malwarescore=0 clxscore=1015\n classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0\n reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605020136", "Received-SPF": "pass client-ip=148.163.158.5;\n envelope-from=amachhiw@linux.ibm.com; helo=mx0b-001b2d01.pphosted.com", "X-Spam_score_int": "-26", "X-Spam_score": "-2.7", "X-Spam_bar": "--", "X-Spam_report": "(-2.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1,\n DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7,\n RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001,\n SPF_PASS=-0.001 autolearn=ham autolearn_force=no", "X-Spam_action": "no action", "X-BeenThere": "qemu-ppc@nongnu.org", "X-Mailman-Version": "2.1.29", "Precedence": "list", "List-Id": "<qemu-ppc.nongnu.org>", "List-Unsubscribe": "<https://lists.nongnu.org/mailman/options/qemu-ppc>,\n <mailto:qemu-ppc-request@nongnu.org?subject=unsubscribe>", "List-Archive": "<https://lists.nongnu.org/archive/html/qemu-ppc>", "List-Post": "<mailto:qemu-ppc@nongnu.org>", "List-Help": "<mailto:qemu-ppc-request@nongnu.org?subject=help>", "List-Subscribe": "<https://lists.nongnu.org/mailman/listinfo/qemu-ppc>,\n <mailto:qemu-ppc-request@nongnu.org?subject=subscribe>", "Errors-To": "qemu-ppc-bounces+incoming=patchwork.ozlabs.org@nongnu.org", "Sender": "qemu-ppc-bounces+incoming=patchwork.ozlabs.org@nongnu.org" }, "content": "On POWER systems, newer processor generations can operate in compatibility\nmodes corresponding to earlier generations (e.g., a Power11 system running\nin Power10 compatibility mode). In such cases, the effective CPU level\nexposed to guests differs from the physical processor generation.\n\nThis creates issues for nested virtualization. When booting a nested KVM\nguest, QEMU may derive the CPU model from the raw hardware PVR and attempt\nto configure the guest accordingly. However, the host is constrained by the\ncompatibility level negotiated with the hypervisor, and requests exceeding\nthat level are rejected by KVM, leading to guest boot failures such as:\n\n KVM-NESTEDv2: couldn't set guest wide elements\n\nThis series addresses the issue in two ways:\n\n1. Do not silently fall back to raw mode when KVM rejects a requested\n compatibility level during CAS. Instead, propagate the error so invalid\n configurations are visible and fail early.\n\n2. Query the effective CPU compatibility modes supported by the host via\n KVM and use this information to select an appropriate CPU model for\n nested guests.\n\nWith these changes, QEMU avoids masking KVM errors and ensures that nested\nguests are configured with CPU models consistent with the host\ncompatibility mode, allowing them to boot correctly.\n\nPatch summary:\n [1/3] hw/ppc/spapr: Do not fallback to raw mode when KVM rejects compat\n [2/3] [DO_NOT_MERGE] linux-headers: Add uapi header changes\n [3/3] target/ppc/kvm: Use host compatibility mode for nested guests\n\nChanges in v2:\n- Patch 3: Guard compatibility mode code with #if defined(TARGET_PPC64)\n to fix compilation for ppc32 targets. The POWER9/10/11 PVR constants\n are only defined for 64-bit builds, and compatibility modes are only\n relevant for 64-bit systems.\n\nTested on:\n - Power11 pSeries LPAR in Power10 compatibility mode\n - Power10 PowerNV and QEMU PowerNV 11 TCG L0 host\n\nCI test results: https://gitlab.com/amachhiw/qemu/-/pipelines/2494987253\n\nNote: Patch 2 is marked DO_NOT_MERGE as it contains linux-headers updates\nthat will be synced separately once the corresponding kernel patches are\nmerged.\n\nThe corresponding Linux patches have been posted [1]\n\n[1] https://lore.kernel.org/all/20260430054906.94431-1-amachhiw@linux.ibm.com/\n\nAmit Machhiwal (3):\n hw/ppc/spapr: Do not fallback to raw mode when KVM rejects compat\n [DO_NOT_MERGE] linux-headers: Add uapi header changes\n target/ppc/kvm: Use host compatibility mode for nested guests\n\n hw/ppc/spapr_hcall.c | 9 ++++++\n linux-headers/asm-powerpc/kvm.h | 7 ++++\n linux-headers/linux/kvm.h | 3 ++\n target/ppc/kvm.c | 57 +++++++++++++++++++++++++++++++++\n 4 files changed, 76 insertions(+)\n\n\nbase-commit: 3d626609ccae61a2e552bccd59c7a0931bab8261" }