From: Madhavan Srinivasan <maddy@linux.ibm.com>
To: linuxppc-dev@lists.ozlabs.org, Amit Machhiwal <amachhiw@linux.ibm.com>
Cc: Vaibhav Jain <vaibhav@linux.ibm.com>,
Anushree Mathur <anushree.mathur@linux.ibm.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Nicholas Piggin <npiggin@gmail.com>,
Michael Ellerman <mpe@ellerman.id.au>,
"Christophe Leroy (CS GROUP)" <chleroy@kernel.org>,
Jonathan Corbet <corbet@lwn.net>,
Shuah Khan <skhan@linuxfoundation.org>,
Ritesh Harjani <ritesh.list@gmail.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org,
Harsh Prateek Bora <harshpb@linux.ibm.com>,
Gautam Menghani <gautam@linux.ibm.com>
Subject: Re: [PATCH v9 0/4] KVM: PPC: Expose CPU compatibility modes for nested guests
Date: Tue, 11 Aug 2026 10:23:20 +0530 [thread overview]
Message-ID: <178642395406.173296.2879693080941807837.b4-ty@linux.ibm.com> (raw)
In-Reply-To: <20260808161148.66673-1-amachhiw@linux.ibm.com>
On Sat, 08 Aug 2026 21:41:44 +0530, Amit Machhiwal wrote:
> On POWER systems, newer processor generations can operate in compatibility
> modes corresponding to earlier generations (e.g., a Power11 system running
> in Power10 compatibility mode). In such cases, the effective CPU level
> exposed to guests differs from the physical processor generation.
>
> This creates a problem for nested virtualization. When booting a nested KVM
> guest (L2) inside a host KVM guest (L1) running in a compatibility mode,
> userspace (e.g., QEMU) may derive the CPU model from the raw hardware PVR
> and attempt to configure the nested guest accordingly. However, the L1
> partition is constrained by the compatibility level negotiated with the
> hypervisor (L0), and requests exceeding that level are rejected, leading to
> guest boot failures such as:
>
> [...]
Applied to powerpc/next.
[1/4] KVM: PPC: Introduce KVM_CAP_PPC_COMPAT_CAPS and wire up ioctl
https://git.kernel.org/powerpc/c/ac3e65ddddf3128c1f0c2187889fab458fcf4a70
[2/4] KVM: PPC: Book3S HV: Implement compat CPU capability retrieval for KVM on PowerVM
https://git.kernel.org/powerpc/c/b76fb087efcdaf6eb5c2c6c5e53c763640fc4b02
[3/4] KVM: PPC: Book3S HV: Add support for compat CPU capabilities for KVM on PowerNV
https://git.kernel.org/powerpc/c/8735048f54ec827102dcbd757a6c1c1e02613fc4
[4/4] KVM: PPC: Document KVM_PPC_GET_COMPAT_CAPS ioctl
https://git.kernel.org/powerpc/c/c1721e584244ff79a593d6f0ad0405a2e07b765a
cheers
prev parent reply other threads:[~2026-08-11 4:53 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-08 16:11 [PATCH v9 0/4] KVM: PPC: Expose CPU compatibility modes for nested guests Amit Machhiwal
2026-08-08 16:11 ` [PATCH v9 1/4] KVM: PPC: Introduce KVM_CAP_PPC_COMPAT_CAPS and wire up ioctl Amit Machhiwal
2026-08-08 16:11 ` [PATCH v9 2/4] KVM: PPC: Book3S HV: Implement compat CPU capability retrieval for KVM on PowerVM Amit Machhiwal
2026-08-08 16:11 ` [PATCH v9 3/4] KVM: PPC: Book3S HV: Add support for compat CPU capabilities for KVM on PowerNV Amit Machhiwal
2026-08-08 16:11 ` [PATCH v9 4/4] KVM: PPC: Document KVM_PPC_GET_COMPAT_CAPS ioctl Amit Machhiwal
2026-08-11 4:53 ` Madhavan Srinivasan [this message]
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