On 09.04.2018 09:26, Jidong Xiao wrote: > 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! > Oh, by the way, I just realized that we actually have for nested VMX launch_state contained in "struct __packed vmcs12", so it is indeed contained in the VMCS region for nested VMX! "Any VMX implementation has a VMCS structure, and vmcs12 is our emulated VMX's VMCS" Sorry I missed that before! -- Thanks, David / dhildenb
