VMX: VMentry failure with branch tracing and blocked states

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For XSA-308 logic was introduced, as VMX VMEntry checks do not like the exact combination of state which occurs when #DB in intercepted, Single Stepping is active, and blocked by STI/MovSS is active, despite this being a legitimate state to be in. The resulting VMEntry failure is fatal to the guest. Sadly there is another special sub-case of the above, with branch tracing enabled. In that case the prior adjustment would still cause a VMentry failure, as before fatal to the guest.

Source published

13 Oct 2026 15:44:56 UTC

Source modified

20 Oct 2026 17:31:41 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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