KVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN

Summary

In the Linux kernel, the following vulnerability has been resolved: KVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN Don't reset the VMCB's TLB control back to "do nothing" on a failed VMRUN, as empirical testing shows that the CPU performs the requested TLB flush if and only if VMRUN is successful, i.e. clearing TLB control on a failed VMRUN effectively drops a TLB flush. Explicitly track the need to flush all ASIDs on a per-CPU basis, as the ASID reuse condition is tied to the pCPU, not to the vCPU. As a bonus, this also obviates the need to avoid clobbering FLUSH_ALL_ASID with TLB_CONTROL_FLUSH_ASID, e.g. in svm_flush_tlb_asid(). Deliberately don't bother saving/restoring the "old" tlb_ctl on failure, in quotes because it's not exactly the old tlb_ctl, it's the tlb_ctl from after pre_svm_run(), but before updating tlb_ctl for flush_all_asids. If VMRUN fails and TLB_CONTROL_FLUSH_ALL_ASID is forced, then the next successful run of the VMCB may unnecessarily flush all ASIDs, which strictly speaking could result in noisy neighbor issues. However, the fact that new_asid() is already guest-triggerable, because of KVM's flawed behavior of clearing the ASID on emulated INIT, means that a guest can already trigger a flush of all ASIDs at roughly the same rate. And once KVM stops clobbering the ASID on emulated INIT, or assigns a static ASID to each vCPU, this flaw goes away.

Timeline

1. Oct 18, 2026, 3:46 PM UTCCVE published
2. Oct 19, 2026, 9:24 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 38e5e92fe8c02a8766459d505423b855caf9af1f · fixed in fd873c3d1b5240e80365f09e758e8c96b88a7cdb; From 38e5e92fe8c02a8766459d505423b855caf9af1f · fixed in 60d93c27859fb3ec5b5a689e24de303f166477d0

• Linux Linux

  2.6.38

• KernelLinux

  From 2.6.38 · fixed in 7.2.10

References 2