VPID is used to tag address space and avoid a TLB flush. Currently L0 use
the same VPID to run L1 and all its guests. KVM flushes VPID when switching
between L1 and L2.
This patch advertises VPID to the L1 hypervisor, then address space of L1 and
L2 can be separately treated and avoid TLB flush when swithing between L1 and
L2. For each nested vmentry, if vpid12 is changed, reuse shadow vpid w/ an
invvpid.
Performance:
run lmbench on L2 w/ 3.5 kernel.
Context switching - times in microseconds - smaller is better
-------------------------------------------------------------------------
Host OS 2p/0K 2p/16K 2p/64K 8p/16K 8p/64K 16p/16K 16p/64K
ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw
--------- ------------- ------ ------ ------ ------ ------ ------- -------
kernel Linux 3.5.0-1 1.2200 1.3700 1.4500 4.7800 2.3300 5.60000 2.88000 nested VPID
kernel Linux 3.5.0-1 1.2600 1.4300 1.5600 12.7 12.9 3.49000 7.46000 vanilla
Suggested-by: Wincy Van <fanwenyi0529@xxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
---
arch/x86/kvm/vmx.c | 25 ++++++++++++++++++-------
1 file changed, 18 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index bd07d88..6d8ec00 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -425,6 +425,7 @@ struct nested_vmx {
u64 vmcs01_debugctl;
u16 vpid02;
+ u16 last_vpid;
u32 nested_vmx_procbased_ctls_low;
u32 nested_vmx_procbased_ctls_high;
@@ -1159,6 +1160,11 @@ static inline bool nested_cpu_has_virt_x2apic_mode(struct vmcs12 *vmcs12)
return nested_cpu_has2(vmcs12, SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE);
}
+static inline bool nested_cpu_has_vpid(struct vmcs12 *vmcs12)
+{
+ return nested_cpu_has2(vmcs12, SECONDARY_EXEC_ENABLE_VPID);
+}
+
static inline bool nested_cpu_has_apic_reg_virt(struct vmcs12 *vmcs12)
{
return nested_cpu_has2(vmcs12, SECONDARY_EXEC_APIC_REGISTER_VIRT);
@@ -2473,6 +2479,7 @@ static void nested_vmx_setup_ctls_msrs(struct vcpu_vmx *vmx)
SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
SECONDARY_EXEC_RDTSCP |
SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE |
+ SECONDARY_EXEC_ENABLE_VPID |
SECONDARY_EXEC_APIC_REGISTER_VIRT |
SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
SECONDARY_EXEC_WBINVD_EXITING |
@@ -9460,13 +9467,17 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
vmcs_write64(TSC_OFFSET, vmx->nested.vmcs01_tsc_offset);
if (enable_vpid) {
- /*
- * Trivially support vpid by letting L2s share their parent
- * L1's vpid. TODO: move to a more elaborate solution, giving
- * each L2 its own vpid and exposing the vpid feature to L1.
- */
- vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
- vmx_flush_tlb(vcpu);
+ if (nested_cpu_has_vpid(vmcs12)) {
+ vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->nested.vpid02);
+ if (vmcs12->virtual_processor_id != vmx->nested.last_vpid) {
+ vmx->nested.last_vpid = vmcs12->virtual_processor_id;
+ vmx_flush_tlb(vcpu);
+ }
+ } else {
+ vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
+ vmx_flush_tlb(vcpu);
+ }
+
}
if (nested_cpu_has_ept(vmcs12)) {
--
1.9.1
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