Messages in this thread | | | Subject | Re: [PATCH] KVM: nVMX: nested VPID emulation | From | Wanpeng Li <> | Date | Tue, 15 Sep 2015 18:14:57 +0800 |
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On 9/14/15 10:54 PM, Jan Kiszka wrote: > On 2015-09-14 14:52, Wanpeng Li wrote: >> 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. This patch gets ~3x performance improvement for lmbench 8p/64k ctxsw. >> >> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> >> --- >> arch/x86/kvm/vmx.c | 39 ++++++++++++++++++++++++++++++++------- >> 1 file changed, 32 insertions(+), 7 deletions(-) >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index da1590e..06bc31e 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -1157,6 +1157,11 @@ 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); >> @@ -2471,6 +2476,7 @@ 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 | >> @@ -4160,7 +4166,7 @@ static void allocate_vpid(struct vcpu_vmx *vmx) >> int vpid; >> >> vmx->vpid = 0; >> - if (!enable_vpid) >> + if (!enable_vpid || is_guest_mode(&vmx->vcpu)) >> return; >> spin_lock(&vmx_vpid_lock); >> vpid = find_first_zero_bit(vmx_vpid_bitmap, VMX_NR_VPIDS); >> @@ -6738,6 +6744,14 @@ static int handle_vmclear(struct kvm_vcpu *vcpu) >> } >> vmcs12 = kmap(page); >> vmcs12->launch_state = 0; >> + if (enable_vpid) { >> + if (nested_cpu_has_vpid(vmcs12)) { >> + spin_lock(&vmx_vpid_lock); >> + if (vmcs12->virtual_processor_id != 0) >> + __clear_bit(vmcs12->virtual_processor_id, vmx_vpid_bitmap); >> + spin_unlock(&vmx_vpid_lock); > Maybe enhance free_vpid (and also allocate_vpid) to work generically and > let the caller decide where to take the vpid from or where to store it?
Good idea.
> >> + } >> + } >> kunmap(page); >> nested_release_page(page); >> >> @@ -9189,6 +9203,7 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12) >> { >> struct vcpu_vmx *vmx = to_vmx(vcpu); >> u32 exec_control; >> + int vpid; >> >> vmcs_write16(GUEST_ES_SELECTOR, vmcs12->guest_es_selector); >> vmcs_write16(GUEST_CS_SELECTOR, vmcs12->guest_cs_selector); >> @@ -9438,13 +9453,21 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12) >> else >> 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); >> + if (nested_cpu_has_vpid(vmcs12)) { >> + if (vmcs12->virtual_processor_id == 0) { >> + spin_lock(&vmx_vpid_lock); >> + vpid = find_first_zero_bit(vmx_vpid_bitmap, VMX_NR_VPIDS); >> + if (vpid < VMX_NR_VPIDS) >> + __set_bit(vpid, vmx_vpid_bitmap); >> + spin_unlock(&vmx_vpid_lock); >> + vmcs_write16(VIRTUAL_PROCESSOR_ID, vpid); > It's a bit non-obvious that vpid == VMX_NR_VPIDS (no free vpids) will > lead to vpid == 0 when writing VIRTUAL_PROCESSOR_ID. You should leave at > least a comment. Or generalize allocate_vpid as that one is already > clearer in this regard.
Ditto.
> >> + } else >> + vmcs_write16(VIRTUAL_PROCESSOR_ID, vmcs12->virtual_processor_id); >> + } else >> + vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid); >> + >> vmx_flush_tlb(vcpu); >> } >> >> @@ -9973,6 +9996,8 @@ static void prepare_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12, >> vmcs12_save_pending_event(vcpu, vmcs12); >> } >> >> + if (nested_cpu_has_vpid(vmcs12)) >> + vmcs12->virtual_processor_id = vmcs_read16(VIRTUAL_PROCESSOR_ID); >> /* >> * Drop what we picked up for L2 via vmx_complete_interrupts. It is >> * preserved above and would only end up incorrectly in L1. >> > Last but not least: the guest can now easily exhaust the host's pool of > vpid by simply spawning plenty of VCPUs for L2, no? Is this acceptable > or should there be some limit?
I reuse the value of vpid02 while vpid12 changed w/ one invvpid in v2, and the scenario which you pointed out can be avoid.
Regards, Wanpeng Li
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