linux-kernel - [PATCH v4 02/11] KVM: VMX: Track common EPTP for Hyper-V's paravirt TLB flush

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Message-Id: <20210305183123.3978098-3-seanjc@google.com>
Date:   Fri,  5 Mar 2021 10:31:14 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: [PATCH v4 02/11] KVM: VMX: Track common EPTP for Hyper-V's paravirt
 TLB flush

From: Sean Christopherson <sean.j.christopherson@...el.com>

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.

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 20 +++++++++-----------
 arch/x86/kvm/vmx/vmx.h |  1 +
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index dde2ebc7cf3a..4082c7a26612 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -483,12 +483,14 @@ static void check_ept_pointer_match(struct kvm *kvm)
 		if (!VALID_PAGE(tmp_eptp)) {
 			tmp_eptp = to_vmx(vcpu)->ept_pointer;
 		} else if (tmp_eptp != to_vmx(vcpu)->ept_pointer) {
+			to_kvm_vmx(kvm)->hv_tlb_eptp = INVALID_PAGE;
 			to_kvm_vmx(kvm)->ept_pointers_match
 				= EPT_POINTERS_MISMATCH;
 			return;
 		}
 	}
 
+	to_kvm_vmx(kvm)->hv_tlb_eptp = tmp_eptp;
 	to_kvm_vmx(kvm)->ept_pointers_match = EPT_POINTERS_MATCH;
 }
 
@@ -501,21 +503,18 @@ 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,
@@ -533,12 +532,11 @@ 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 4795955490cb..f846cf3a5d25 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -351,6 +351,7 @@ 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;
 };
-- 
2.30.1.766.gb4fecdf3b7-goog