[PATCH v2 01/10] KVM: VMX: Track common EPTP for Hyper-V's paravirt TLB flush

From: Sean Christopherson
Date: Tue Oct 20 2020 - 17:56:20 EST


Explicitly track the EPTP that is common to all vCPUs instead of
grabbing vCPU0's EPTP when invoking Hyper-V's paravirt TLB flush.
Tracking the EPTP will allow optimizing the checks when loading a new
EPTP and will also allow dropping ept_pointer_match, e.g. by marking
the common EPTP as invalid.

This also technically fixes a bug where KVM could theoretically flush an
invalid GPA if all vCPUs have an invalid root. In practice, it's likely
impossible to trigger a remote TLB flush in such a scenario. In any
case, the superfluous flush is completely benign.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
arch/x86/kvm/vmx/vmx.c | 19 ++++++++-----------
arch/x86/kvm/vmx/vmx.h | 1 +
2 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index bcc097bb8321..6d53bcc4a1a9 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -486,6 +486,7 @@ static void check_ept_pointer_match(struct kvm *kvm)
}
}

+ to_kvm_vmx(kvm)->hv_tlb_eptp = tmp_eptp;
to_kvm_vmx(kvm)->ept_pointers_match = EPT_POINTERS_MATCH;
}

@@ -498,21 +499,18 @@ static int kvm_fill_hv_flush_list_func(struct hv_guest_mapping_flush_list *flush
range->pages);
}

-static inline int __hv_remote_flush_tlb_with_range(struct kvm *kvm,
- struct kvm_vcpu *vcpu, struct kvm_tlb_range *range)
+static inline int hv_remote_flush_eptp(u64 eptp, struct kvm_tlb_range *range)
{
- u64 ept_pointer = to_vmx(vcpu)->ept_pointer;
-
/*
* FLUSH_GUEST_PHYSICAL_ADDRESS_SPACE hypercall needs address
* of the base of EPT PML4 table, strip off EPT configuration
* information.
*/
if (range)
- return hyperv_flush_guest_mapping_range(ept_pointer & PAGE_MASK,
+ return hyperv_flush_guest_mapping_range(eptp & PAGE_MASK,
kvm_fill_hv_flush_list_func, (void *)range);
else
- return hyperv_flush_guest_mapping(ept_pointer & PAGE_MASK);
+ return hyperv_flush_guest_mapping(eptp & PAGE_MASK);
}

static int hv_remote_flush_tlb_with_range(struct kvm *kvm,
@@ -530,12 +528,11 @@ static int hv_remote_flush_tlb_with_range(struct kvm *kvm,
kvm_for_each_vcpu(i, vcpu, kvm) {
/* If ept_pointer is invalid pointer, bypass flush request. */
if (VALID_PAGE(to_vmx(vcpu)->ept_pointer))
- ret |= __hv_remote_flush_tlb_with_range(
- kvm, vcpu, range);
+ ret |= hv_remote_flush_eptp(to_vmx(vcpu)->ept_pointer,
+ range);
}
- } else {
- ret = __hv_remote_flush_tlb_with_range(kvm,
- kvm_get_vcpu(kvm, 0), range);
+ } else if (VALID_PAGE(to_kvm_vmx(kvm)->hv_tlb_eptp)) {
+ ret = hv_remote_flush_eptp(to_kvm_vmx(kvm)->hv_tlb_eptp, range);
}

spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 5961cb897125..3d557a065c01 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -301,6 +301,7 @@ struct kvm_vmx {
bool ept_identity_pagetable_done;
gpa_t ept_identity_map_addr;

+ hpa_t hv_tlb_eptp;
enum ept_pointers_status ept_pointers_match;
spinlock_t ept_pointer_lock;
};
--
2.28.0