Sean Christopherson <[email protected]> writes:
> On Tue, Sep 25, 2018 at 07:58:39PM +0200, Vitaly Kuznetsov wrote:
>> When EPT is used for nested guest we need to re-init MMU as shadow
>> EPT MMU (nested_ept_init_mmu_context() does that). When we return back
>> from L2 to L1 kvm_mmu_reset_context() in nested_vmx_load_cr3() resets
>> MMU back to normal TDP mode. Add a special 'guest_mmu' so we can use
>> separate root caches; the improved hit rate is not very important for
>> single vCPU performance, but it avoids contention on the mmu_lock for
>> many vCPUs.
>>
>> On the nested CPUID benchmark, with 16 vCPUs, an L2->L1->L2 vmexit
>> goes from 42k to 26k cycles.
>>
>> Signed-off-by: Vitaly Kuznetsov <[email protected]>
>> Signed-off-by: Paolo Bonzini <[email protected]>
>> ---
>> Changes since v1:
>> - drop now unneded local vmx variable in vmx_free_vcpu_nested
>> [Sean Christopherson]
>> ---
>> arch/x86/include/asm/kvm_host.h | 3 +++
>> arch/x86/kvm/mmu.c | 15 +++++++++++----
>> arch/x86/kvm/vmx.c | 27 ++++++++++++++++++---------
>> 3 files changed, 32 insertions(+), 13 deletions(-)
>
> ...
>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 2d55adab52de..93ff08136fc1 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -8468,8 +8468,10 @@ static inline void nested_release_vmcs12(struct
>> vcpu_vmx *vmx)
>> * Free whatever needs to be freed from vmx->nested when L1 goes down, or
>> * just stops using VMX.
>> */
>> -static void free_nested(struct vcpu_vmx *vmx)
>> +static void free_nested(struct kvm_vcpu *vcpu)
>> {
>> + struct vcpu_vmx *vmx = to_vmx(vcpu);
>> +
>> if (!vmx->nested.vmxon && !vmx->nested.smm.vmxon)
>> return;
>>
>> @@ -8502,6 +8504,8 @@ static void free_nested(struct vcpu_vmx *vmx)
>> vmx->nested.pi_desc = NULL;
>> }
>>
>> + kvm_mmu_free_roots(vcpu, &vcpu->arch.guest_mmu, KVM_MMU_ROOTS_ALL);
>> +
>> free_loaded_vmcs(&vmx->nested.vmcs02);
>> }
>>
>> @@ -8510,7 +8514,7 @@ static int handle_vmoff(struct kvm_vcpu *vcpu)
>> {
>> if (!nested_vmx_check_permission(vcpu))
>> return 1;
>> - free_nested(to_vmx(vcpu));
>> + free_nested(vcpu);
>> nested_vmx_succeed(vcpu);
>> return kvm_skip_emulated_instruction(vcpu);
>> }
>> @@ -8541,6 +8545,8 @@ static int handle_vmclear(struct kvm_vcpu *vcpu)
>> if (vmptr == vmx->nested.current_vmptr)
>> nested_release_vmcs12(vmx);
>>
>> + kvm_mmu_free_roots(vcpu, &vcpu->arch.guest_mmu, KVM_MMU_ROOTS_ALL);
>
> Shouldn't we only free guest_mmu if VMCLEAR is targeting
> current_vmptr?
Right you are, this was definitely overlooked, no need for
kvm_mmu_free_roots() when we VMCLEAR some-other-vmptr.
> Assuming that's the case, we could put the call to kvm_mmu_free_roots()
> in nested_release_vmcs12() instead of calling it from handle_vmclear()
> and handle_vmptrld().
Yep, will do in v3.
>
>> +
>> kvm_vcpu_write_guest(vcpu,
>> vmptr + offsetof(struct vmcs12, launch_state),
>> &zero, sizeof(zero));
>> @@ -8924,6 +8930,9 @@ static int handle_vmptrld(struct kvm_vcpu *vcpu)
>> }
>>
>> nested_release_vmcs12(vmx);
>> +
>> + kvm_mmu_free_roots(vcpu, &vcpu->arch.guest_mmu,
>> + KVM_MMU_ROOTS_ALL);
>> /*
>> * Load VMCS12 from guest memory since it is not already
>> * cached.
>> @@ -10976,12 +10985,10 @@ static void vmx_switch_vmcs(struct kvm_vcpu *vcpu,
>> struct loaded_vmcs *vmcs)
>> */
>> static void vmx_free_vcpu_nested(struct kvm_vcpu *vcpu)
>> {
>> - struct vcpu_vmx *vmx = to_vmx(vcpu);
>> -
>> - vcpu_load(vcpu);
>> - vmx_switch_vmcs(vcpu, &vmx->vmcs01);
>> - free_nested(vmx);
>> - vcpu_put(vcpu);
>> + vcpu_load(vcpu);
>> + vmx_switch_vmcs(vcpu, &to_vmx(vcpu)->vmcs01);
>> + free_nested(vcpu);
>> + vcpu_put(vcpu);
>> }
>>
>> static void vmx_free_vcpu(struct kvm_vcpu *vcpu)
>> @@ -11331,6 +11338,7 @@ static int nested_ept_init_mmu_context(struct
>> kvm_vcpu *vcpu)
>> if (!valid_ept_address(vcpu, nested_ept_get_cr3(vcpu)))
>> return 1;
>>
>> + vcpu->arch.mmu = &vcpu->arch.guest_mmu;
>> kvm_init_shadow_ept_mmu(vcpu,
>> to_vmx(vcpu)->nested.msrs.ept_caps &
>> VMX_EPT_EXECUTE_ONLY_BIT,
>> @@ -11346,6 +11354,7 @@ static int nested_ept_init_mmu_context(struct
>> kvm_vcpu *vcpu)
>>
>> static void nested_ept_uninit_mmu_context(struct kvm_vcpu *vcpu)
>> {
>> + vcpu->arch.mmu = &vcpu->arch.root_mmu;
>> vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;
>> }
>>
>> @@ -13421,7 +13430,7 @@ static void vmx_leave_nested(struct kvm_vcpu *vcpu)
>> to_vmx(vcpu)->nested.nested_run_pending = 0;
>> nested_vmx_vmexit(vcpu, -1, 0, 0);
>> }
>> - free_nested(to_vmx(vcpu));
>> + free_nested(vcpu);
>> }
>>
>> /*
>> --
>> 2.17.1
>>
--
Vitaly
