On Mon, Apr 9, 2018 at 1:21 AM, David Hildenbrand <david@xxxxxxxxxx> wrote: > On 09.04.2018 09:17, Jidong Xiao wrote: >> 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. > > Guess as the guest has to way to access it via VMREAD/VMWRITE it doesn't > make any difference, or do you have something in mind? > Oh, because the SDM clearly says it's in the region, but then it doesn't say where exactly it is in the region; so I was just confused. But now I understand. Thanks David! >> >>> >>> -- >>> >>> Thanks, >>> >>> David / dhildenb > > > -- > > Thanks, > > David / dhildenb
