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Tue, 23 Jun 2026 13:30:57 +0000 (GMT) Received: from fedora (unknown [9.5.7.39]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTPS; Tue, 23 Jun 2026 13:30:57 +0000 (GMT) Date: Tue, 23 Jun 2026 19:01:02 +0530 From: Amit Machhiwal To: Vaibhav Jain Cc: Amit Machhiwal , linuxppc-dev@lists.ozlabs.org, Madhavan Srinivasan , Anushree Mathur , Paolo Bonzini , Nicholas Piggin , Michael Ellerman , "Christophe Leroy (CS GROUP)" , Jonathan Corbet , Shuah Khan , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, lkp@intel.com Subject: Re: [PATCH v4 3/4] KVM: PPC: Book3S HV: Add support for compat CPU capabilities for KVM on PowerNV Message-ID: <20260623184241.8e374888-21-amachhiw@linux.ibm.com> Mail-Followup-To: Vaibhav Jain , linuxppc-dev@lists.ozlabs.org, Madhavan Srinivasan , Anushree Mathur , Paolo Bonzini , Nicholas Piggin , Michael Ellerman , "Christophe Leroy (CS GROUP)" , Jonathan Corbet , Shuah Khan , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, lkp@intel.com References: <20260616123314.82721-1-amachhiw@linux.ibm.com> <20260616123314.82721-4-amachhiw@linux.ibm.com> <875x3fcb3x.fsf@vajain21.in.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <875x3fcb3x.fsf@vajain21.in.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: nyXU7o40VOo8V5yxqrQUWxvc1L-b6MUf X-Proofpoint-Spam-Info: AW1haW4tMjYwNjIzMDEwOSBTYWx0ZWRfXwdK4yZxg3rk7 p1REKI3j15iK+1IcH68V/NHd5FUz51uGZWnP2yKdhyRqEh6Gn6Uf8gRWS0qRmfWTX5dwl2E2gN5 gSVzjM0shOSyLVLs1By3dO+pYwUSp8U= X-Authority-Analysis: v=2.4 cv=c62bhx9l c=1 sm=1 tr=0 ts=6a3a8a9a cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=kj9zAlcOel0A:10 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=Zaj4I9ly_lfmcsfu6SgA:9 a=CjuIK1q_8ugA:10 a=O8hF6Hzn-FEA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjIzMDEwOSBTYWx0ZWRfX1DwwukmerMBb Q79TOapNAChYjRlG6GepV10vYtXPVT3wsC/LEm9FDRzoxXksVuI2Ke4bXXSgM4FeEceFV8N8ygq J1dkhQtZuNnw4OwxMXOa2Gdx8BwtBlKsLEHmmH8VXjXavMK0pjXf8gPErojMuC1oQKBj8tGImd5 PzGitMI25rfiIGmnD8bZDRMH4569BLPmYV7YS6BVrLQRDjN58l2LeDfktx+Dt1szeMDIJ7rd9RR pqA+3CTFGr385Dfg7eHhhssOiOdoL2fCi+HRtXszc9EL5tiwmkLOjwWMVXDHxYrD+9GObSvQQoY Nxsvz3UPCwS0yzQDs7ckgURs0+Rov7PGBV5BjfmVT4ZaL7O3k7F7GZ/7w1oceWRUC3ii6gz5+B4 rHNNAfXhDSGOHWx5PFhzPbHbWcM/QFPGNcAbDfhdUNQkqaNGpKIBaLvPXCDuBXnf1XH+ztFIJ3a O4r/u/L0uDFsoXGZBGQ== X-Proofpoint-ORIG-GUID: iBMXzw_zgg5xWl3ffCuCfpbV8dWDmbLf 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=2026-06-23_03,2026-06-23_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 impostorscore=0 adultscore=0 clxscore=1015 suspectscore=0 priorityscore=1501 phishscore=0 spamscore=0 bulkscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2606230109 Hi Vaibhav, Thanks for reviewing this patch. Please find my response inline. On 2026/06/19 11:42 AM, Vaibhav Jain wrote: > Hi Amit. > > Thanks for the patch and incorporating V3 review comments. Further > review comments inline below: > > Amit Machhiwal writes: > > > Currently, when booting a compatibility-mode KVM guest (L1) on a PowerNV > > hypervisor (L0), the guest runs with the expected processor > > compatibility level. However, when booting a nested KVM guest (L2) > > inside the L1, QEMU derives the CPU model from the raw host PVR and > > attempts to run the nested guest at that level, instead of honoring the > > compatibility mode of the L1. > > > > Extend host CPU compatibility capability reporting to support nested > > virtualization on PowerNV systems (PAPR nested API v1). > > > > For nested API v2 (PowerVM), compatibility capabilities are obtained > > from the hypervisor via the H_GUEST_GET_CAPABILITIES hcall. This > > information is not available on PowerNV systems. > > > > For nested API v1, derive the compatibility capabilities from the L1 > > guest by reading the "cpu-version" property from the device tree, which > > reflects the effective (logical) processor compatibility level. Map this > > value to the corresponding compatibility capability bitmap using > > KVM-specific constants. > > > > Introduce a helper to translate CPU version values into KVM_PPC_COMPAT_CAP > > bits and integrate it into kvmppc_get_compat_caps(). The implementation > > applies masking to ensure only supported processor modes are exposed. > > > > This allows userspace to query host CPU compatibility modes on both > > PowerVM and PowerNV platforms via the KVM_PPC_GET_COMPAT_CAPS ioctl. > > > > Suggested-by: Vaibhav Jain > > Signed-off-by: Amit Machhiwal > > --- > > arch/powerpc/kvm/book3s_hv.c | 37 +++++++++++++++++++++++++++++++++++- > > 1 file changed, 36 insertions(+), 1 deletion(-) > > > > diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c > > index f674386df62c..375e7a7fa9f8 100644 > > --- a/arch/powerpc/kvm/book3s_hv.c > > +++ b/arch/powerpc/kvm/book3s_hv.c > > @@ -6523,15 +6523,50 @@ static bool kvmppc_hash_v3_possible(void) > > return true; > > } > > > > +static int kvmppc_map_compat_capabilities(const __be32 cpu_version, > > + unsigned long *capabilities) > > +{ > > + switch (cpu_version) { > > + case PVR_ARCH_31_P11: > > + *capabilities |= KVM_PPC_COMPAT_CAP_POWER11; > Do you need to do 'break' here instead of falling through. Since P11 > host can support P10 and P9 compat modes I had addressed a similar comment from Harsh in v1 of the series here: https://lore.kernel.org/all/20260507202740.96fb259f-22-amachhiw@linux.ibm.com/ The current implementation with break statements is intentional. This function (kvmppc_map_compat_capabilities()) is called only when booting a nested KVM guest (L2) on **KVM on PowerNV**. When the L1 KVM guest is booted in a compat mode, L2 is supposed to boot with the **same PVR version** as that of the L1, which is already taken care of with the current changes. If L2 needs to boot with a different *lower* compat mode, it would use max-cpu-compat, which takes a different code path for setting the compat. Even if I included all lower compat modes in the compat caps **APIv1**, I don't think we'll be using those lower compat bits unless we wanted to block a specific older compat for a given pvr level - which neither we are doing in this series nor we may want to put such a restriction for APIv1. Please let me know if you think otherwise. > > > + break; > > + case PVR_ARCH_31: > > + *capabilities |= KVM_PPC_COMPAT_CAP_POWER10; > > + break; > > + case PVR_ARCH_300: > > + *capabilities |= KVM_PPC_COMPAT_CAP_POWER9; > > + break; > > + default: > > + return -EINVAL; > > + } > > + > > + return 0; > > +} > > > > static int kvmppc_get_compat_caps(struct kvm_ppc_compat_caps *host_caps) > > { > > + struct device_node *np; > > unsigned long capabilities = 0; > > + const __be32 *prop = NULL; > > long rc = -EINVAL; > > + u32 cpu_version; > > > > if (kvmhv_on_pseries()) { > > - if (kvmhv_is_nestedv2()) > > + if (kvmhv_is_nestedv2()) { > > rc = plpar_guest_get_capabilities(0, &capabilities); > > + } else { > > + for_each_node_by_type(np, "cpu") { > > + prop = of_get_property(np, "cpu-version", NULL); > > + if (prop) { > > + cpu_version = be32_to_cpup(prop); > > + break; > > + } > > + } > > + if (!prop) > > + return -EINVAL; > > + rc = kvmppc_map_compat_capabilities(cpu_version, > > + &capabilities); > > + } > should you check for 'rc' error here before assigning 'capabilities' to > 'host_caps->compat_capabilities' . I understand it will be set to '0' > due to its initialization at the top of the function. But would be > better to make it more explicit Sure. The return value rc is checked by the caller but more error checking is always good I guess. :) I'll add a check for rc something like this (or something similar): if (rc) { return -EINVAL; } host_caps->compat_capabilities = capabilities & KVM_PPC_COMPAT_BITMASK; Thanks, Amit > > > host_caps->compat_capabilities = capabilities & > > KVM_PPC_COMPAT_BITMASK; > > } > > -- > > 2.50.1 (Apple Git-155) > > > > > > -- > Cheers > ~ Vaibhav