diff options
author | Sean Christopherson <sean.j.christopherson@intel.com> | 2019-01-25 07:41:02 -0800 |
---|---|---|
committer | Paolo Bonzini <pbonzini@redhat.com> | 2019-02-12 13:12:22 +0100 |
commit | 5a8781607e677eda60b20e0a4c91d2a5f12f9244 (patch) | |
tree | 3ad19b2b68799e509703628520ae4b20f498df7f /arch/x86/kvm/vmx/vmcs.h | |
parent | fbda0fd31a6d683637f848ba17956048dd0c7e48 (diff) |
KVM: nVMX: Cache host_rsp on a per-VMCS basis
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>
Diffstat (limited to 'arch/x86/kvm/vmx/vmcs.h')
-rw-r--r-- | arch/x86/kvm/vmx/vmcs.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/x86/kvm/vmx/vmcs.h b/arch/x86/kvm/vmx/vmcs.h index 6def3ba88e3b..cb6079f8a227 100644 --- a/arch/x86/kvm/vmx/vmcs.h +++ b/arch/x86/kvm/vmx/vmcs.h @@ -34,6 +34,7 @@ struct vmcs_host_state { unsigned long cr4; /* May not match real cr4 */ unsigned long gs_base; unsigned long fs_base; + unsigned long rsp; u16 fs_sel, gs_sel, ldt_sel; #ifdef CONFIG_X86_64 |