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x86/kvm/mmu: introduce guest_mmu
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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 <vkuznets@redhat.com>
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Vitaly Kuznetsov authored and Paolo Bonzini committed Oct 16, 2018
1 parent 6a82cd1 commit 14c07ad
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Showing 3 changed files with 40 additions and 18 deletions.
3 changes: 3 additions & 0 deletions arch/x86/include/asm/kvm_host.h
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Original file line number Diff line number Diff line change
Expand Up @@ -548,6 +548,9 @@ struct kvm_vcpu_arch {
/* Non-nested MMU for L1 */
struct kvm_mmu root_mmu;

/* L1 MMU when running nested */
struct kvm_mmu guest_mmu;

/*
* Paging state of an L2 guest (used for nested npt)
*
Expand Down
20 changes: 15 additions & 5 deletions arch/x86/kvm/mmu.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4832,7 +4832,10 @@ EXPORT_SYMBOL_GPL(kvm_init_shadow_mmu);
static union kvm_mmu_page_role
kvm_calc_shadow_ept_root_page_role(struct kvm_vcpu *vcpu, bool accessed_dirty)
{
union kvm_mmu_page_role role = vcpu->arch.mmu->base_role;
union kvm_mmu_page_role role;

/* Role is inherited from root_mmu */
role.word = vcpu->arch.root_mmu.base_role.word;

role.level = PT64_ROOT_4LEVEL;
role.direct = false;
Expand Down Expand Up @@ -4982,8 +4985,10 @@ EXPORT_SYMBOL_GPL(kvm_mmu_load);

void kvm_mmu_unload(struct kvm_vcpu *vcpu)
{
kvm_mmu_free_roots(vcpu, vcpu->arch.mmu, KVM_MMU_ROOTS_ALL);
WARN_ON(VALID_PAGE(vcpu->arch.mmu->root_hpa));
kvm_mmu_free_roots(vcpu, &vcpu->arch.root_mmu, KVM_MMU_ROOTS_ALL);
WARN_ON(VALID_PAGE(vcpu->arch.root_mmu.root_hpa));
kvm_mmu_free_roots(vcpu, &vcpu->arch.guest_mmu, KVM_MMU_ROOTS_ALL);
WARN_ON(VALID_PAGE(vcpu->arch.guest_mmu.root_hpa));
}
EXPORT_SYMBOL_GPL(kvm_mmu_unload);

Expand Down Expand Up @@ -5422,13 +5427,18 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)

vcpu->arch.mmu = &vcpu->arch.root_mmu;
vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;

vcpu->arch.root_mmu.root_hpa = INVALID_PAGE;
vcpu->arch.root_mmu.translate_gpa = translate_gpa;
vcpu->arch.nested_mmu.translate_gpa = translate_nested_gpa;

for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++)
vcpu->arch.root_mmu.prev_roots[i] = KVM_MMU_ROOT_INFO_INVALID;

vcpu->arch.guest_mmu.root_hpa = INVALID_PAGE;
vcpu->arch.guest_mmu.translate_gpa = translate_gpa;
for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++)
vcpu->arch.guest_mmu.prev_roots[i] = KVM_MMU_ROOT_INFO_INVALID;

vcpu->arch.nested_mmu.translate_gpa = translate_nested_gpa;
return alloc_mmu_pages(vcpu);
}

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35 changes: 22 additions & 13 deletions arch/x86/kvm/vmx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -8423,8 +8423,10 @@ static void vmx_disable_shadow_vmcs(struct vcpu_vmx *vmx)
vmcs_write64(VMCS_LINK_POINTER, -1ull);
}

static inline void nested_release_vmcs12(struct vcpu_vmx *vmx)
static inline void nested_release_vmcs12(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);

if (vmx->nested.current_vmptr == -1ull)
return;

Expand All @@ -8438,19 +8440,23 @@ static inline void nested_release_vmcs12(struct vcpu_vmx *vmx)
vmx->nested.posted_intr_nv = -1;

/* Flush VMCS12 to guest memory */
kvm_vcpu_write_guest_page(&vmx->vcpu,
kvm_vcpu_write_guest_page(vcpu,
vmx->nested.current_vmptr >> PAGE_SHIFT,
vmx->nested.cached_vmcs12, 0, VMCS12_SIZE);

kvm_mmu_free_roots(vcpu, &vcpu->arch.guest_mmu, KVM_MMU_ROOTS_ALL);

vmx->nested.current_vmptr = -1ull;
}

/*
* 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;

Expand Down Expand Up @@ -8483,6 +8489,8 @@ 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);
}

Expand All @@ -8491,7 +8499,7 @@ static int handle_vmoff(struct kvm_vcpu *vcpu)
{
if (!nested_vmx_check_permission(vcpu))
return 1;
free_nested(to_vmx(vcpu));
free_nested(vcpu);
return nested_vmx_succeed(vcpu);
}

Expand All @@ -8517,7 +8525,7 @@ static int handle_vmclear(struct kvm_vcpu *vcpu)
VMXERR_VMCLEAR_VMXON_POINTER);

if (vmptr == vmx->nested.current_vmptr)
nested_release_vmcs12(vmx);
nested_release_vmcs12(vcpu);

kvm_vcpu_write_guest(vcpu,
vmptr + offsetof(struct vmcs12, launch_state),
Expand Down Expand Up @@ -8872,7 +8880,8 @@ static int handle_vmptrld(struct kvm_vcpu *vcpu)
VMXERR_VMPTRLD_INCORRECT_VMCS_REVISION_ID);
}

nested_release_vmcs12(vmx);
nested_release_vmcs12(vcpu);

/*
* Load VMCS12 from guest memory since it is not already
* cached.
Expand Down Expand Up @@ -10928,12 +10937,10 @@ 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)
Expand Down Expand Up @@ -11300,6 +11307,7 @@ static void nested_ept_init_mmu_context(struct kvm_vcpu *vcpu)
{
WARN_ON(mmu_is_nested(vcpu));

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,
Expand All @@ -11315,6 +11323,7 @@ static void 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;
}

Expand Down Expand Up @@ -13731,7 +13740,7 @@ 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);
}

static int vmx_check_intercept(struct kvm_vcpu *vcpu,
Expand Down

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