In the context switch logic Xen attempts to skip an IBPB in the case of a vCPU returning to a CPU on which it was the previous vCPU to run. While safe for Xen's isolation between vCPUs, this prevents the guest kernel correctly isolating between tasks. Consider:
1) vCPU runs on CPU A, running task 1. 2) vCPU moves to CPU B, idle gets scheduled on A. Xen skips IBPB. 3) On CPU B, guest kernel switches from task 1 to 2, issuing IBPB. 4) vCPU moves back to CPU A. Xen skips IBPB again.
Now, task 2 is running on CPU A with task 1's training still in the BTB.
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Alpine Linux | — | Upgrade xen | Jan 29, 2026 | Jan 28, 2026 |
| Debian | — | Upgrade xen | Jul 23, 2026 | Jan 28, 2026 |
| Suse | — | Upgrade xen-libsUpgrade xen-toolsUpgrade xen-develUpgrade xen-libs-32bitUpgrade xenUpgrade xen-tools-xendomains-wait-diskUpgrade xen-tools-domUUpgrade xen-doc-html | Jan 28, 2026 | Jan 28, 2026 |
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