On Mon, Apr 9, 2018 at 1:10 AM, David Hildenbrand <david@xxxxxxxxxx> wrote: > On 09.04.2018 06:21, Jidong Xiao wrote: >> Hi, >> >> The Intel SDM says: >> >> "The launch state of a VMCS determines which VM-entry instruction >> should be used with that VMCS: the >> VMLAUNCH instruction requires a VMCS whose launch state is “clear”; >> the VMRESUME instruction requires a VMCS >> whose launch state is “launched”. A logical processor maintains a >> VMCS’s launch state in the corresponding VMCS >> region." >> >> "There are no other ways to modify the launch state of a VMCS (it >> cannot be modified using VMWRITE) and there >> is no direct way to discover it (it cannot be read using VMREAD).' >> >> According to the above description, the launch state is stored in the >> VMCS region, but it seems the SDM doesn't say where exactly the launch >> state is stored in the VMCS. For example, the VMCS data is organized >> into six logic groups: Guest-state area, Host-state area, VM-execution >> control fields, VM-exit control fields, VM-entry control fields, >> VM-exit information fields. However, I can't find the "launch state" >> in any of these fields. >> >> If it's in the VMCS region, then why can't I find it? and why it can't >> be discovered by VMREAD? > > Why do you assume the launch state has to be stored inside the VMCS region? > > It is just being stated that you cannot detect/modify it via > VMWRITE/VMREAD. Which is perfectly true if the launch state is stored > outside of the VMCS region. > > What the SDM states here simply is that the caller has to remember if a > VMCS has already been launched. This is what we do with the "launched" > variable. > > And this is also what we use for emulation of VMLAUNCH/VMRESUME in > nested_vmx_run(). > >> >> I saw in the kvm source code a variable called launched is defined, >> which enables kvm to trace the launch state of the VMCS, but is this >> launch state really existing in the VMCS region? If so, where exactly >> is it? > > Nope, not in the region, it's glued to struct loaded_vmcs. > Oh, okay, thanks David, I see. The reason I assumed it's in the VMCS region is because the SDM says: "A logical processor maintains a VMCS’s launch state in the corresponding VMCS region." Since it's not really in the region, I guess the SDM is inaccurate on this. > > -- > > Thanks, > > David / dhildenb
