Currently, host_rsp is cached on a per-vCPU basis, i.e. it's stored in
struct vcpu_vmx. In non-nested usage the caching is for all intents
and purposes 100% effective, e.g. only the first VMLAUNCH needs to
synchronize VMCS.HOST_RSP since the call stack to vmx_vcpu_run() is
identical each and every time. But when running a nested guest, KVM
must invalidate the cache when switching the current VMCS as it can't
guarantee the new VMCS has the same HOST_RSP as the previous VMCS. In
other words, the cache loses almost all of its efficacy when running a
nested VM.
Move host_rsp to struct vmcs_host_state, which is per-VMCS, so that it
is cached on a per-VMCS basis and restores its 100% hit rate when
nested VMs are in play.
Note that the host_rsp cache for vmcs02 essentially "breaks" when
nested early checks are enabled as nested_vmx_check_vmentry_hw() will
see a different RSP at the time of its VM-Enter. While it's possible
to avoid even that VMCS.HOST_RSP synchronization, e.g. by employing a
dedicated VM-Exit stack, there is little motivation for doing so as
the overhead of two VMWRITEs (~55 cycles) is dwarfed by the overhead
of the extra VMX transition (600+ cycles) and is a proverbial drop in
the ocean relative to the total cost of a nested transtion (10s of
thousands of cycles).
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The header, evmcs.h, already exists and contains a fair amount of code,
but there are a few pieces in vmx.c that can be moved verbatim. In
addition, move an array definition to evmcs.c to prepare for multiple
consumers of evmcs.h.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
vmcs12 is the KVM-defined struct used to track a nested VMCS, e.g. a
VMCS created by L1 for L2.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This isn't intended to be a pure reflection of hardware, e.g. struct
loaded_vmcs and struct vmcs_host_state are KVM-defined constructs.
Similar to capabilities.h, this is a standalone file to avoid circular
dependencies between yet-to-be-created vmx.h and nested.h files.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Sean Christopherson