Re: [PATCH v2 24/25] KVM: x86/mmu: initialize constant-value fields just once

Sean Christopherson
2022-03-08T20:58:56Z

On Mon, Feb 21, 2022, Paolo Bonzini wrote:
>
> + vcpu->arch.root_mmu.get_guest_pgd = kvm_get_guest_cr3;
> + vcpu->arch.root_mmu.get_pdptr = kvm_pdptr_read;
> +
> + if (tdp_enabled) {

Putting all this code is in a separate helper reduces line-lengths via early
returns. And it'll allow us to do the same for the nested specific MMUs if we
ever get smart and move "nested" to x86.c (preferably as enable_nested or
nested_enabled).

> + vcpu->arch.root_mmu.inject_page_fault = kvm_inject_page_fault;
> + vcpu->arch.root_mmu.page_fault = kvm_tdp_page_fault;
> + vcpu->arch.root_mmu.sync_page = nonpaging_sync_page;
> + vcpu->arch.root_mmu.invlpg = NULL;
> + reset_tdp_shadow_zero_bits_mask(&vcpu->arch.root_mmu);
> +
> + vcpu->arch.guest_mmu.get_guest_pgd = kvm_x86_ops.nested_ops->get_nested_pgd;
> + vcpu->arch.guest_mmu.get_pdptr = kvm_x86_ops.nested_ops->get_nested_pdptr;
> + vcpu->arch.guest_mmu.inject_page_fault = kvm_x86_ops.nested_ops->inject_nested_tdp_vmexit;

Using nested_ops is clever, but IMO unnecessary, especially since we can go even
further by adding a nEPT specific hook to initialize its constant shadow paging
stuff.

Here's what I had written spliced in with your code. Compile tested only for
this version.

From: Paolo Bonzini <pbonzini@redhat.com>
Date: Mon, 21 Feb 2022 11:22:42 -0500
Subject: [PATCH] KVM: x86/mmu: initialize constant-value fields just once

The get_guest_pgd, get_pdptr and inject_page_fault pointers are constant
for all three of root_mmu, guest_mmu and nested_mmu. The guest_mmu
function pointers depend on the processor vendor, but are otherwise
constant.

Opportunistically stop initializing get_pdptr for nested EPT, since it
does not have PDPTRs.

Opportunistically change kvm_mmu_create() to return '0' unconditionally
in its happy path to make it obvious that it's a happy path.

Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/mmu.h | 1 +
arch/x86/kvm/mmu/mmu.c | 85 ++++++++++++++++++++++++---------------
arch/x86/kvm/svm/nested.c | 15 +++++--
arch/x86/kvm/svm/svm.c | 3 ++
arch/x86/kvm/svm/svm.h | 1 +
arch/x86/kvm/vmx/nested.c | 13 ++++--
arch/x86/kvm/vmx/nested.h | 1 +
arch/x86/kvm/vmx/vmx.c | 3 ++
8 files changed, 82 insertions(+), 40 deletions(-)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 9517e56a0da1..bd2a6e20307c 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -71,6 +71,7 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only);
void kvm_init_mmu(struct kvm_vcpu *vcpu);
void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, unsigned long cr0,
unsigned long cr4, u64 efer, gpa_t nested_cr3);
+void kvm_init_shadow_ept_mmu_constants(struct kvm_vcpu *vcpu);
void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
int huge_page_level, bool accessed_dirty,
gpa_t new_eptp);
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 8c388add95cb..db2d88c59198 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4778,12 +4778,6 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu,

context->cpu_mode.as_u64 = cpu_mode.as_u64;
context->root_role.word = root_role.word;
- context->page_fault = kvm_tdp_page_fault;
- context->sync_page = nonpaging_sync_page;
- context->invlpg = NULL;
- context->get_guest_pgd = kvm_get_guest_cr3;
- context->get_pdptr = kvm_pdptr_read;
- context->inject_page_fault = kvm_inject_page_fault;

if (!is_cr0_pg(context))
context->gva_to_gpa = nonpaging_gva_to_gpa;
@@ -4793,7 +4787,6 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu,
context->gva_to_gpa = paging32_gva_to_gpa;

reset_guest_paging_metadata(vcpu, context);
- reset_tdp_shadow_zero_bits_mask(context);
}

static void shadow_mmu_init_context(struct kvm_vcpu *vcpu, struct kvm_mmu *context,
@@ -4818,8 +4811,8 @@ static void shadow_mmu_init_context(struct kvm_vcpu *vcpu, struct kvm_mmu *conte
reset_shadow_zero_bits_mask(vcpu, context);
}

-static void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu,
- union kvm_mmu_paging_mode cpu_mode)
+static void init_kvm_softmmu(struct kvm_vcpu *vcpu,
+ union kvm_mmu_paging_mode cpu_mode)
{
struct kvm_mmu *context = &vcpu->arch.root_mmu;
union kvm_mmu_page_role root_role;
@@ -4891,6 +4884,17 @@ kvm_calc_shadow_ept_root_page_role(struct kvm_vcpu *vcpu, bool accessed_dirty,
return role;
}

+void kvm_init_shadow_ept_mmu_constants(struct kvm_vcpu *vcpu)
+{
+ struct kvm_mmu *guest_mmu = &vcpu->arch.guest_mmu;
+
+ guest_mmu->page_fault = ept_page_fault;
+ guest_mmu->gva_to_gpa = ept_gva_to_gpa;
+ guest_mmu->sync_page = ept_sync_page;
+ guest_mmu->invlpg = ept_invlpg;
+}
+EXPORT_SYMBOL_GPL(kvm_init_shadow_ept_mmu_constants);
+
void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
int huge_page_level, bool accessed_dirty,
gpa_t new_eptp)
@@ -4912,7 +4916,6 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
context->invlpg = ept_invlpg;

update_permission_bitmask(context, true);
- context->pkru_mask = 0;
reset_rsvds_bits_mask_ept(vcpu, context, execonly, huge_page_level);
reset_ept_shadow_zero_bits_mask(context, execonly);
}
@@ -4921,18 +4924,6 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
}
EXPORT_SYMBOL_GPL(kvm_init_shadow_ept_mmu);

-static void init_kvm_softmmu(struct kvm_vcpu *vcpu,
- union kvm_mmu_paging_mode cpu_mode)
-{
- struct kvm_mmu *context = &vcpu->arch.root_mmu;
-
- kvm_init_shadow_mmu(vcpu, cpu_mode);
-
- context->get_guest_pgd = kvm_get_guest_cr3;
- context->get_pdptr = kvm_pdptr_read;
- context->inject_page_fault = kvm_inject_page_fault;
-}
-
static void init_kvm_nested_mmu(struct kvm_vcpu *vcpu,
union kvm_mmu_paging_mode new_mode)
{
@@ -4941,16 +4932,7 @@ static void init_kvm_nested_mmu(struct kvm_vcpu *vcpu,
if (new_mode.as_u64 == g_context->cpu_mode.as_u64)
return;

- g_context->cpu_mode.as_u64 = new_mode.as_u64;
- g_context->get_guest_pgd = kvm_get_guest_cr3;
- g_context->get_pdptr = kvm_pdptr_read;
- g_context->inject_page_fault = kvm_inject_page_fault;
-
- /*
- * L2 page tables are never shadowed, so there is no need to sync
- * SPTEs.
- */
- g_context->invlpg = NULL;
+ g_context->cpu_mode.as_u64 = new_mode.as_u64;

/*
* Note that arch.mmu->gva_to_gpa translates l2_gpa to l1_gpa using
@@ -5499,6 +5481,40 @@ static void free_mmu_pages(struct kvm_mmu *mmu)
free_page((unsigned long)mmu->pml5_root);
}

+static void kvm_init_mmu_constants(struct kvm_vcpu *vcpu)
+{
+ struct kvm_mmu *nested_mmu = &vcpu->arch.nested_mmu;
+ struct kvm_mmu *root_mmu = &vcpu->arch.root_mmu;
+
+ root_mmu->get_guest_pgd = kvm_get_guest_cr3;
+ root_mmu->get_pdptr = kvm_pdptr_read;
+ root_mmu->inject_page_fault = kvm_inject_page_fault;
+
+ /*
+ * When shadowing IA32 page tables, all other callbacks various based
+ * on paging mode, and the guest+nested MMUs are unused.
+ */
+ if (!tdp_enabled)
+ return;
+
+ root_mmu->page_fault = kvm_tdp_page_fault;
+ root_mmu->sync_page = nonpaging_sync_page;
+ root_mmu->invlpg = NULL;
+ reset_tdp_shadow_zero_bits_mask(&vcpu->arch.root_mmu);
+
+ /*
+ * Nested TDP MMU callbacks that are constant are vendor specific due
+ * to the vast differences between EPT and NPT. NPT in particular is
+ * nasty because L1 may use 32-bit and/or 64-bit paging.
+ */
+ nested_mmu->get_guest_pgd = kvm_get_guest_cr3;
+ nested_mmu->get_pdptr = kvm_pdptr_read;
+ nested_mmu->inject_page_fault = kvm_inject_page_fault;
+
+ /* L2 page tables are never shadowed, there's no need to sync SPTEs. */
+ nested_mmu->invlpg = NULL;
+}
+
static int __kvm_mmu_create(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
{
struct page *page;
@@ -5575,7 +5591,10 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)
if (ret)
goto fail_allocate_root;

- return ret;
+ kvm_init_mmu_constants(vcpu);
+
+ return 0;
+
fail_allocate_root:
free_mmu_pages(&vcpu->arch.guest_mmu);
return ret;
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index dd942c719cf6..c58c9d876a6c 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -96,6 +96,15 @@ static unsigned long nested_svm_get_tdp_cr3(struct kvm_vcpu *vcpu)
return svm->nested.ctl.nested_cr3;
}

+void nested_svm_init_mmu_constants(struct kvm_vcpu *vcpu)
+{
+ struct kvm_mmu *guest_mmu = &vcpu->arch.guest_mmu;
+
+ guest_mmu->get_guest_pgd = nested_svm_get_tdp_cr3;
+ guest_mmu->get_pdptr = nested_svm_get_tdp_pdptr;
+ guest_mmu->inject_page_fault = nested_svm_inject_npf_exit;
+}
+
static void nested_svm_init_mmu_context(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
@@ -112,10 +121,8 @@ static void nested_svm_init_mmu_context(struct kvm_vcpu *vcpu)
kvm_init_shadow_npt_mmu(vcpu, X86_CR0_PG, svm->vmcb01.ptr->save.cr4,
svm->vmcb01.ptr->save.efer,
svm->nested.ctl.nested_cr3);
- vcpu->arch.mmu->get_guest_pgd = nested_svm_get_tdp_cr3;
- vcpu->arch.mmu->get_pdptr = nested_svm_get_tdp_pdptr;
- vcpu->arch.mmu->inject_page_fault = nested_svm_inject_npf_exit;
- vcpu->arch.walk_mmu = &vcpu->arch.nested_mmu;
+
+ vcpu->arch.walk_mmu = &vcpu->arch.nested_mmu;
}

static void nested_svm_uninit_mmu_context(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index a8ee949b2403..db62b3e88317 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1228,6 +1228,9 @@ static int svm_vcpu_create(struct kvm_vcpu *vcpu)

svm->guest_state_loaded = false;

+ if (npt_enabled && nested)
+ nested_svm_init_mmu_constants(vcpu);
+
return 0;

error_free_vmsa_page:
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index e45b5645d5e0..99c5a57ab5dd 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -564,6 +564,7 @@ void nested_copy_vmcb_save_to_cache(struct vcpu_svm *svm,
void nested_sync_control_from_vmcb02(struct vcpu_svm *svm);
void nested_vmcb02_compute_g_pat(struct vcpu_svm *svm);
void svm_switch_vmcb(struct vcpu_svm *svm, struct kvm_vmcb_info *target_vmcb);
+void nested_svm_init_mmu_constants(struct kvm_vcpu *vcpu);

extern struct kvm_x86_nested_ops svm_nested_ops;

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index cc4c74339d35..385f60305555 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -407,15 +407,22 @@ static void nested_ept_new_eptp(struct kvm_vcpu *vcpu)
nested_ept_get_eptp(vcpu));
}

+void nested_ept_init_mmu_constants(struct kvm_vcpu *vcpu)
+{
+ struct kvm_mmu *mmu = &vcpu->arch.guest_mmu;
+
+ mmu->get_guest_pgd = nested_ept_get_eptp;
+ mmu->inject_page_fault = nested_ept_inject_page_fault;
+
+ kvm_init_shadow_ept_mmu_constants(vcpu);
+}
+
static void nested_ept_init_mmu_context(struct kvm_vcpu *vcpu)
{
WARN_ON(mmu_is_nested(vcpu));

vcpu->arch.mmu = &vcpu->arch.guest_mmu;
nested_ept_new_eptp(vcpu);
- vcpu->arch.mmu->get_guest_pgd = nested_ept_get_eptp;
- vcpu->arch.mmu->inject_page_fault = nested_ept_inject_page_fault;
- vcpu->arch.mmu->get_pdptr = kvm_pdptr_read;

vcpu->arch.walk_mmu = &vcpu->arch.nested_mmu;
}
diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
index c92cea0b8ccc..78e6d9ba5839 100644
--- a/arch/x86/kvm/vmx/nested.h
+++ b/arch/x86/kvm/vmx/nested.h
@@ -37,6 +37,7 @@ void nested_vmx_pmu_refresh(struct kvm_vcpu *vcpu,
void nested_mark_vmcs12_pages_dirty(struct kvm_vcpu *vcpu);
bool nested_vmx_check_io_bitmaps(struct kvm_vcpu *vcpu, unsigned int port,
int size);
+void nested_ept_init_mmu_constants(struct kvm_vcpu *vcpu);

static inline struct vmcs12 *get_vmcs12(struct kvm_vcpu *vcpu)
{
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 40e015e9b260..04edb8a761a8 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7081,6 +7081,9 @@ static int vmx_vcpu_create(struct kvm_vcpu *vcpu)
goto free_vmcs;
}

+ if (enable_ept && nested)
+ nested_ept_init_mmu_constants(vcpu);
+
return 0;

free_vmcs:

base-commit: 94fd8078bd4f838cf9ced265e6ac4237cbcba7a1
--