Messages in this thread | | | Subject | Re: [PATCH] KVM: nVMX: nested VPID emulation | From | Wanpeng Li <> | Date | Tue, 15 Sep 2015 18:18:32 +0800 |
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On 9/15/15 12:08 AM, Bandan Das wrote: > Wanpeng Li <wanpeng.li@hotmail.com> writes: > >> 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. > TLB flush does context invalidation and while that should result in > some improvement, I never expected a 3x improvement for any workload! > Interesting :)
The result still looks good when test v2.
> >> 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); >> + } >> + } >> kunmap(page); >> nested_release_page(page); > I don't think this is enough, we should also check for set "nested" bits > in free_vpid() and clear them. There should be some sort of a mapping between the > nested guest vpid and the actual vpid so that we can just clear those bits.
Agreed.
> >> @@ -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); >> >> + > Empty space here. > >> 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) { > Ok, so if we advertise vpid to the nested hypervisor, isn't it going to > attempt writing this field when setting up ? Atleast > that's what Linux does, no ?
Agreed, I do the allocation of vpid02 during initialization in v2.
> >> + 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); >> + } else >> + vmcs_write16(VIRTUAL_PROCESSOR_ID, vmcs12->virtual_processor_id); >> + } else >> + vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid); >> + > I guess L1 shouldn't know what vpid L0 chose to run L2. If L1 vmreads, > it should get what it expects for the value of vpid, not the one L0 chose.
Agreed.
> >> vmx_flush_tlb(vcpu); >> } > So, this isn't removed ? I thought it's not needed anymore ?
Please review v2. :-)
Regards, Wanpeng Li
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