Fix V2 extended topology enumeration APIC ID reporting#7495
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likebreath merged 1 commit intocloud-hypervisor:mainfrom Nov 21, 2025
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Fix V2 extended topology enumeration APIC ID reporting#7495likebreath merged 1 commit intocloud-hypervisor:mainfrom
likebreath merged 1 commit intocloud-hypervisor:mainfrom
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When booting a Linux guest in SMP configuration, on sapphire rapids and granite rapids the following kernel warning can be observed: [Firmware Bug]: CPUID leaf 0x1f subleaf 1 APIC ID mismatch 1 != 0 [Firmware Bug]: CPUID leaf 0x1f subleaf 2 APIC ID mismatch 1 != 0 The reason is that we announce the presence of the extended topology leaf, but fail to announce the x2apic ID in EDX for each subleaf. Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de> On-behalf-of: SAP thomas.prescher@sap.com
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| u32::from(cores_per_die * threads_per_core), | ||
| ); | ||
| CpuidPatch::set_cpuid_reg(cpuid, 0x1f, Some(1), CpuidReg::ECX, 2 << 8); | ||
| CpuidPatch::set_cpuid_reg(cpuid, 0x1f, Some(1), CpuidReg::EDX, x2apic_id); |
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Out of curiosity: what's the index here (Some(1)) and why do we need the same code multiple times? What's the bigger picture?
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It's what the Intel ® Architecture Instruction Set Extensions and Future Features demands.
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I'm not sure where this risc-v pipeline error is coming from, but it is certainly unrelated to these changes. |
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Right. The Risc-v support is still experimental and their runners are flaky sometime. That's s why they are optional. |
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When booting a Linux guest in SMP configuration, on sapphire rapids and granite rapids the following kernel warning can be observed:
The reason is that we announce the presence of the extended topology leaf, but fail to announce the x2apic ID in EDX for each sub-leaf.
We already fixed this for leaf 0xb, sub-leaf zero in #7087, but forgot to do the same for leaf 0x1f and its sub-leafs.
The documentation for this cpuid leaf states the following for EDX: It is always valid and does not vary with the sub-leaf index in ECX