[PATCH v11 28/46] KVM: nSVM: hyper-v: Enable L2 TLB flush

Vitaly Kuznetsov
2022-10-04T12:51:04Z

Implement Hyper-V L2 TLB flush for nSVM. The feature needs to be enabled
both in extended 'nested controls' in VMCB and VP assist page.
According to Hyper-V TLFS, synthetic vmexit to L1 is performed with
- HV_SVM_EXITCODE_ENL exit_code.
- HV_SVM_ENL_EXITCODE_TRAP_AFTER_FLUSH exit_info_1.

Note: VP assist page is cached in 'struct kvm_vcpu_hv' so
recalc_intercepts() doesn't need to read from guest's memory. KVM
needs to update the case upon each VMRUN and after svm_set_nested_state
(svm_get_nested_state_pages()) to handle the case when the guest got
migrated while L2 was running.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/include/asm/hyperv-tlfs.h | 4 ++++
arch/x86/kvm/hyperv.h | 11 ++++++++++
arch/x86/kvm/svm/hyperv.c | 7 ++++++
arch/x86/kvm/svm/hyperv.h | 15 +++++++++++++
arch/x86/kvm/svm/nested.c | 35 ++++++++++++++++++++++++++++--
5 files changed, 70 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
index b25c6792d409..e3efaf6e6b62 100644
--- a/arch/x86/include/asm/hyperv-tlfs.h
+++ b/arch/x86/include/asm/hyperv-tlfs.h
@@ -631,6 +631,10 @@ struct hv_vmcb_enlightenments {
*/
#define HV_VMCB_NESTED_ENLIGHTENMENTS 31

+/* Synthetic VM-Exit */
+#define HV_SVM_EXITCODE_ENL 0xf0000000
+#define HV_SVM_ENL_EXITCODE_TRAP_AFTER_FLUSH (1)
+
struct hv_partition_assist_pg {
u32 tlb_lock_count;
};
diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
index 5157622c2fb3..9f96414a31c5 100644
--- a/arch/x86/kvm/hyperv.h
+++ b/arch/x86/kvm/hyperv.h
@@ -198,6 +198,17 @@ static inline bool kvm_hv_is_tlb_flush_hcall(struct kvm_vcpu *vcpu)
code == HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX);
}

+static inline int kvm_hv_verify_vp_assist(struct kvm_vcpu *vcpu)
+{
+ if (!to_hv_vcpu(vcpu))
+ return 0;
+
+ if (!kvm_hv_assist_page_enabled(vcpu))
+ return 0;
+
+ return kvm_hv_get_assist_page(vcpu);
+}
+
int kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu);

#endif
diff --git a/arch/x86/kvm/svm/hyperv.c b/arch/x86/kvm/svm/hyperv.c
index 911f51021af1..088f6429b24c 100644
--- a/arch/x86/kvm/svm/hyperv.c
+++ b/arch/x86/kvm/svm/hyperv.c
@@ -8,4 +8,11 @@

void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu)
{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
+ svm->vmcb->control.exit_code = HV_SVM_EXITCODE_ENL;
+ svm->vmcb->control.exit_code_hi = 0;
+ svm->vmcb->control.exit_info_1 = HV_SVM_ENL_EXITCODE_TRAP_AFTER_FLUSH;
+ svm->vmcb->control.exit_info_2 = 0;
+ nested_svm_vmexit(svm);
}
diff --git a/arch/x86/kvm/svm/hyperv.h b/arch/x86/kvm/svm/hyperv.h
index 7564bdf652e4..02f4784b5d44 100644
--- a/arch/x86/kvm/svm/hyperv.h
+++ b/arch/x86/kvm/svm/hyperv.h
@@ -25,6 +25,21 @@ static inline void nested_svm_hv_update_vm_vp_ids(struct kvm_vcpu *vcpu)
hv_vcpu->nested.vp_id = hve->hv_vp_id;
}

+static inline bool nested_svm_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+ struct hv_vmcb_enlightenments *hve = &svm->nested.ctl.hv_enlightenments;
+ struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+
+ if (!hv_vcpu)
+ return false;
+
+ if (!hve->hv_enlightenments_control.nested_flush_hypercall)
+ return false;
+
+ return hv_vcpu->vp_assist_page.nested_control.features.directhypercall;
+}
+
void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu);

#endif /* __ARCH_X86_KVM_SVM_HYPERV_H__ */
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 05889d5a8629..8f67b8fb3c1f 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -149,8 +149,12 @@ void recalc_intercepts(struct vcpu_svm *svm)
vmcb_clr_intercept(c, INTERCEPT_VINTR);
}

- /* We don't want to see VMMCALLs from a nested guest */
- vmcb_clr_intercept(c, INTERCEPT_VMMCALL);
+ /*
+ * We want to see VMMCALLs from a nested guest only when Hyper-V L2 TLB
+ * flush feature is enabled.
+ */
+ if (!nested_svm_l2_tlb_flush_enabled(&svm->vcpu))
+ vmcb_clr_intercept(c, INTERCEPT_VMMCALL);

for (i = 0; i < MAX_INTERCEPT; i++)
c->intercepts[i] |= g->intercepts[i];
@@ -472,6 +476,15 @@ static void nested_save_pending_event_to_vmcb12(struct vcpu_svm *svm,

static void nested_svm_transition_tlb_flush(struct kvm_vcpu *vcpu)
{
+ /*
+ * KVM_REQ_HV_TLB_FLUSH flushes entries from either L1's VP_ID or
+ * L2's VP_ID upon request from the guest. Make sure we check for
+ * pending entries in the right FIFO upon L1/L2 transition as these
+ * requests are put by other vCPUs asynchronously.
+ */
+ if (to_hv_vcpu(vcpu) && npt_enabled)
+ kvm_make_request(KVM_REQ_HV_TLB_FLUSH, vcpu);
+
/*
* TODO: optimize unconditional TLB flush/MMU sync. A partial list of
* things to fix before this can be conditional:
@@ -823,6 +836,13 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
return 1;
}

+ /* This fails when VP assist page is enabled but the supplied GPA is bogus */
+ ret = kvm_hv_verify_vp_assist(vcpu);
+ if (ret) {
+ kvm_inject_gp(vcpu, 0);
+ return ret;
+ }
+
vmcb12_gpa = svm->vmcb->save.rax;
ret = kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map);
if (ret == -EINVAL) {
@@ -1412,6 +1432,7 @@ static int svm_check_nested_events(struct kvm_vcpu *vcpu)
int nested_svm_exit_special(struct vcpu_svm *svm)
{
u32 exit_code = svm->vmcb->control.exit_code;
+ struct kvm_vcpu *vcpu = &svm->vcpu;

switch (exit_code) {
case SVM_EXIT_INTR:
@@ -1430,6 +1451,13 @@ int nested_svm_exit_special(struct vcpu_svm *svm)
return NESTED_EXIT_HOST;
break;
}
+ case SVM_EXIT_VMMCALL:
+ /* Hyper-V L2 TLB flush hypercall is handled by L0 */
+ if (guest_hv_cpuid_has_l2_tlb_flush(vcpu) &&
+ nested_svm_l2_tlb_flush_enabled(vcpu) &&
+ kvm_hv_is_tlb_flush_hcall(vcpu))
+ return NESTED_EXIT_HOST;
+ break;
default:
break;
}
@@ -1710,6 +1738,9 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
return false;
}

+ if (kvm_hv_verify_vp_assist(vcpu))
+ return false;
+
return true;
}

--
2.37.3