Conceptually, this series is fairly simple: the host's FS/GS selector
and base values rarely change, so only update their corresponding VMCS
fields when necessary. VMWRITE takes ~27 cycles on modern hardware,
i.e. eliminating writes to HOST_{FS,GS}_{SEL,BASE} can save upwards of
~100 cycles when reloading a vCPU after an exit to userspace.
The actual optimization is implemented in the final two patches. The
preceding nine patches are a mix of refactoring and cleansing; KVM's
FS/GS related code in particular has become a bit crusty as KVM has
evolved over the years.
Sean Christopherson (11):
KVM: vmx: move msr_host_bndcfgs out of struct host_state
KVM: vmx: refactor segmentation code in vmx_save_host_state()
KVM: vmx: track host_state.loaded using a loaded_vmcs pointer
KVM: vmx: add dedicated utility to access guest's kernel_gs_base
KVM: vmx: rename __vmx_load_host_state() and vmx_save_host_state()
KVM: nVMX: remove a misleading comment regarding vmcs02 fields
KVM: vmx: compute need to reload FS/GS/LDT on demand
KVM: vmx: move struct host_state usage to struct loaded_vmcs
KVM: vmx: always initialize HOST_{FS,GS}_BASE to zero during setup
KVM: vmx: skip VMWRITE of HOST_{FS,GS}_SEL when possible
KVM: vmx: skip VMWRITE of HOST_{FS,GS}_BASE when possible
arch/x86/kvm/vmx.c | 246 ++++++++++++++++++++++++++-------------------
1 file changed, 144 insertions(+), 102 deletions(-)
--
2.18.0
