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? > >> >> -- >> >> Thanks, >> >> David / dhildenb -- Thanks, David / dhildenb
