KVM: nVMX: Introduce vmcs02: VMCS used to run L2
We saw in a previous patch that L1 controls its L2 guest with a vcms12. L0 needs to create a real VMCS for running L2. We call that "vmcs02". A later patch will contain the code, prepare_vmcs02(), for filling the vmcs02 fields. This patch only contains code for allocating vmcs02. In this version, prepare_vmcs02() sets *all* of vmcs02's fields each time we enter from L1 to L2, so keeping just one vmcs02 for the vcpu is enough: It can be reused even when L1 runs multiple L2 guests. However, in future versions we'll probably want to add an optimization where vmcs02 fields that rarely change will not be set each time. For that, we may want to keep around several vmcs02s of L2 guests that have recently run, so that potentially we could run these L2s again more quickly because less vmwrites to vmcs02 will be needed. This patch adds to each vcpu a vmcs02 pool, vmx->nested.vmcs02_pool, which remembers the vmcs02s last used to run up to VMCS02_POOL_SIZE L2s. As explained above, in the current version we choose VMCS02_POOL_SIZE=1, I.e., one vmcs02 is allocated (and loaded onto the processor), and it is reused to enter any L2 guest. In the future, when prepare_vmcs02() is optimized not to set all fields every time, VMCS02_POOL_SIZE should be increased. Signed-off-by: Nadav Har'El <nyh@il.ibm.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
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