On Fri, Feb 16, 2018 at 04:23:33PM +0100, KarimAllah Ahmed wrote: > On 02/16/2018 03:52 PM, Paolo Bonzini wrote: > > On 16/02/2018 15:23, KarimAllah Ahmed wrote: > > > On exit to L0 user-space, always exit from L2 to L1 and synchronize the > > > state properly for L1. This ensures that user-space only ever sees L1 > > > state. It also allows L1 to be saved and resumed properly. Obviously > > > horrible things will still happen to the L2 guest. This will be handled in > > > a seperate patch. > > > > > > There is only a single case which requires a bit of extra care. When the > > > decision to switch to user space happens while handling an L1 > > > VMRESUME/VMLAUNCH (i.e. pending_nested_run). In order to handle this > > > as cleanly as possible without major restructuring, we simply do not exit > > > to user-space in this case and give L2 another chance to actually run. We > > > also request an immediate exit to ensure that an exit to user space will > > > still happen for the L2. > > > > > > The only reason I can see where an exit to user space will occur while L2 > > > is running is because of a pending signal. The is how user space preempts > > > the KVM_RUN in order to save the state. L2 exits are either handled in L0 > > > kernel or reflected to L1 and not handled in L0 user-space. > > > > > > Signed-off-by: KarimAllah Ahmed <karahmed@xxxxxxxxx> > > > > We discussed this with Jim about one year ago and then again last > > January. While I (in 2017) and David H. (in 2018) also thought about > > doing an L2->L1 exit like this, Jim quickly got me to change my > > mind---it doesn't really seem like a good idea compared to doing full > > checkpointing of VMX state. You can find the discussion at > > https://patchwork.kernel.org/patch/9454799/. > > > > Of course, Jim's series (first posted Nov 2016) is way more complex than > > yours, but the good news is that most of his changes have already been > > merged; the only ones missing are: > > > > https://patchwork.kernel.org/patch/9454799/ > > [7/8] kvm: nVMX: Introduce KVM_CAP_VMX_STATE > > > > https://patchwork.kernel.org/patch/9454797/ > > [8/8] kvm: nVMX: Defer gpa->hpa lookups for set_vmx_state > > Oh! Thank you for pointing this out. Somehow I did not notice any of this :) > > I was also thinking about doing a full save of VMX state then I decided > to do the switch instead. > > In any case, Looking forward to see those bits in master. .. Is somebody working on this or would it make sense to have a couple of folks work together on this?
