On 09/01/2018 17:48, Liran Alon wrote: >>> >>> + if (have_spec_ctrl) { >>> + rdmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl); >>> + if (vmx->spec_ctrl != 0) >>> + wrmsrl(MSR_IA32_SPEC_CTRL, 0); > > As I said also on the AMD patch, I think this is a bug. > Intel specify that we should set IBRS bit even if it was already set on every #VMExit. That's correct (though I'd like to understand _why_---I'm not inclined to blindly trust a spec), but for now it's saving a wrmsr of 0. That is quite obviously okay, and will be also okay after the bare-metal IBRS patches. Of course the code will become something like if (using_ibrs || vmx->spec_ctrl != 0) wrmsrl(MSR_IA32_SPEC_CTRL, host_ibrs); optimizing the case where the host is using retpolines. Paolo