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charset="us-ascii" On Wed, Oct 21, 2026, Hao Zhang wrote: > From: Hao Zhang > > Intel allows SYSENTER in both IA-32e submodes, whereas AMD raises #UD > in either submode. On AMD hosts, KVM intercepts #UD and emulates > SYSENTER to support Intel-compatible vCPUs. > > However, em_sysenter() unconditionally rejects execution from 64-bit > mode. As a result, a valid SYSENTER in an Intel-compatible guest can > fail emulation instead of entering the guest's kernel. For a > non-nested guest at CPL0, this results in a > KVM_INTERNAL_ERROR_EMULATION exit to userspace even when > KVM_CAP_EXIT_ON_EMULATION_FAILURE is not enabled. > > Remove the unconditional rejection. Why? I'm not inclined to expand the emulator's capabilities for something like this without a *really* good reason to do so.