Paolo Bonzini <[email protected]> wrote: > 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.
Excuse my ignorance: Can you point me to the specifications that mention “we should set IBRS bit even if it was already set on every #VMExit” ? Thanks, Nadav
