linux-kernel - [PATCH 18/18] KVM: x86: Add a fastpath handler for INVD

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Message-ID: <20250805190526.1453366-19-seanjc@google.com>
Date: Tue,  5 Aug 2025 12:05:26 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, Xin Li <xin@...or.com>, 
	Dapeng Mi <dapeng1.mi@...ux.intel.com>, Sandipan Das <sandipan.das@....com>
Subject: [PATCH 18/18] KVM: x86: Add a fastpath handler for INVD

Add a fastpath handler for INVD so that the common fastpath logic can be
trivially tested on both Intel and AMD.  Under KVM, INVD is always:
(a) intercepted, (b) available to the guest, and (c) emulated as a nop,
with no side effects.  Combined with INVD not having any inputs or outputs,
i.e. no register constraints, INVD is the perfect instruction for
exercising KVM's fastpath as it can be inserted into practically any
guest-side code stream.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 2 ++
 arch/x86/kvm/vmx/vmx.c | 2 ++
 arch/x86/kvm/x86.c     | 9 +++++++++
 arch/x86/kvm/x86.h     | 1 +
 4 files changed, 14 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 829d9d46718d..f7e1e665a826 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4200,6 +4200,8 @@ static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
 		return handle_fastpath_set_msr_irqoff(vcpu);
 	case SVM_EXIT_HLT:
 		return handle_fastpath_hlt(vcpu);
+	case SVM_EXIT_INVD:
+		return handle_fastpath_invd(vcpu);
 	default:
 		break;
 	}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index aa157fe5b7b3..95765db52992 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7175,6 +7175,8 @@ static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu,
 		return handle_fastpath_preemption_timer(vcpu, force_immediate_exit);
 	case EXIT_REASON_HLT:
 		return handle_fastpath_hlt(vcpu);
+	case EXIT_REASON_INVD:
+		return handle_fastpath_invd(vcpu);
 	default:
 		return EXIT_FASTPATH_NONE;
 	}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a56f83b40a55..5af2c5aed0f2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2086,6 +2086,15 @@ int kvm_emulate_invd(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_emulate_invd);
 
+fastpath_t handle_fastpath_invd(struct kvm_vcpu *vcpu)
+{
+	if (!kvm_emulate_invd(vcpu))
+		return EXIT_FASTPATH_EXIT_USERSPACE;
+
+	return EXIT_FASTPATH_REENTER_GUEST;
+}
+EXPORT_SYMBOL_GPL(handle_fastpath_invd);
+
 int kvm_handle_invalid_op(struct kvm_vcpu *vcpu)
 {
 	kvm_queue_exception(vcpu, UD_VECTOR);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index bcfd9b719ada..46220b04cdf2 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -439,6 +439,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 			    int emulation_type, void *insn, int insn_len);
 fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu);
 fastpath_t handle_fastpath_hlt(struct kvm_vcpu *vcpu);
+fastpath_t handle_fastpath_invd(struct kvm_vcpu *vcpu);
 
 extern struct kvm_caps kvm_caps;
 extern struct kvm_host_values kvm_host;
-- 
2.50.1.565.gc32cd1483b-goog