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 The main request was to make [7/8] a bit more generic so that it can be applied to SVM as well. That's pretty simple though. Thanks, Paolo
