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.
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
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