Messages in this thread |  | | Date | Wed, 6 May 2026 12:17:24 -0500 | | Subject | Re: [PATCH v1 0/2] x86/amd_node: harden amd_smn_init() against Xen dom0 topology | | From | Mario Limonciello <> |
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On 5/6/26 00:55, Penny Zheng wrote: > While booting a recent linux-next kernel as a Xen PVH dom0 on x86, the kernel > oopses very early during fs_initcall: > > Oops: divide error: 0000 [#1] SMP NOPTI > RIP: 0010:amd_smn_init+0x188/0x2e0 > > Followed: on a kernel that survives the divide, it will fail by a NULL pointer > dereference from the first SMN consumer (amd_pmc_probe -> amd_smn_read).
So to confirm - does amd_pmc_probe work properly with this series now?
> > Root cause > ========== > > To prevent each dom0 vCPU from looking like an SMT sibling of another > vCPU, Xen synthesizes guest x2APIC IDs as vcpu_index * 2. This spacing every > vCPU's APIC ID by 2 can push the synthesized IDs past the package-field > boundary. Linux then infers more "packages" and therefore more AMD > nodes via amd_num_nodes() than the platform actually has, while the > PCI-side host-bridge scan correctly reports the number of root complex. > > The fixes are tested on Xen 4.20 PVH dom0 on AMD Zen (16 vCPUs) on top of > linux-next/master (next-20260505). > > Penny Zheng (2): > x86/amd_node: avoid divide-by-zero in amd_smn_init() under Xen dom0 > x86/amd_node: reject SMN access when amd_smn_init() did not complete > > arch/x86/kernel/amd_node.c | 23 ++++++++++++++++++++--- > 1 file changed, 20 insertions(+), 3 deletions(-) >
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