linux-kernel - [PATCH v4] KVM: x86: inhibit APICv when KVM_GUESTDBG

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Date:   Mon,  8 Nov 2021 11:02:45 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Jim Mattson <jmattson@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Maxim Levitsky <mlevitsk@...hat.com>,
        Borislav Petkov <bp@...en8.de>
Subject: [PATCH v4] KVM: x86: inhibit APICv when KVM_GUESTDBG_BLOCKIRQ active

KVM_GUESTDBG_BLOCKIRQ relies on interrupts being injected using
standard kvm's inject_pending_event, and not via APICv/AVIC.

Since this is a debug feature, just inhibit APICv/AVIC while
KVM_GUESTDBG_BLOCKIRQ is in use on at least one vCPU.

Fixes: 61e5f69ef0837 ("KVM: x86: implement KVM_GUESTDBG_BLOCKIRQ")

Reported-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
Reviewed-and-tested-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/svm/avic.c         |  3 ++-
 arch/x86/kvm/vmx/vmx.c          |  3 ++-
 arch/x86/kvm/x86.c              | 20 ++++++++++++++++++++
 4 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 88fce6ab4bbd7..8f6e15b95a4d8 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1034,6 +1034,7 @@ struct kvm_x86_msr_filter {
 #define APICV_INHIBIT_REASON_IRQWIN     3
 #define APICV_INHIBIT_REASON_PIT_REINJ  4
 #define APICV_INHIBIT_REASON_X2APIC	5
+#define APICV_INHIBIT_REASON_BLOCKIRQ	6
 
 struct kvm_arch {
 	unsigned long n_used_mmu_pages;
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 8052d92069e01..affc0ea98d302 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -904,7 +904,8 @@ bool svm_check_apicv_inhibit_reasons(ulong bit)
 			  BIT(APICV_INHIBIT_REASON_NESTED) |
 			  BIT(APICV_INHIBIT_REASON_IRQWIN) |
 			  BIT(APICV_INHIBIT_REASON_PIT_REINJ) |
-			  BIT(APICV_INHIBIT_REASON_X2APIC);
+			  BIT(APICV_INHIBIT_REASON_X2APIC) |
+			  BIT(APICV_INHIBIT_REASON_BLOCKIRQ);
 
 	return supported & BIT(bit);
 }
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 71f54d85f104c..e4fc9ff7cd944 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7565,7 +7565,8 @@ static void hardware_unsetup(void)
 static bool vmx_check_apicv_inhibit_reasons(ulong bit)
 {
 	ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
-			  BIT(APICV_INHIBIT_REASON_HYPERV);
+			  BIT(APICV_INHIBIT_REASON_HYPERV) |
+			  BIT(APICV_INHIBIT_REASON_BLOCKIRQ);
 
 	return supported & BIT(bit);
 }
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ac83d873d65b0..6064ac47c8a37 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10703,6 +10703,24 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
 	return ret;
 }
 
+static void kvm_arch_vcpu_guestdbg_update_apicv_inhibit(struct kvm *kvm)
+{
+	bool inhibit = false;
+	struct kvm_vcpu *vcpu;
+	int i;
+
+	down_write(&kvm->arch.apicv_update_lock);
+
+	kvm_for_each_vcpu(i, vcpu, kvm) {
+		if (vcpu->guest_debug & KVM_GUESTDBG_BLOCKIRQ) {
+			inhibit = true;
+			break;
+		}
+	}
+	__kvm_request_apicv_update(kvm, !inhibit, APICV_INHIBIT_REASON_BLOCKIRQ);
+	up_write(&kvm->arch.apicv_update_lock);
+}
+
 int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 					struct kvm_guest_debug *dbg)
 {
@@ -10755,6 +10773,8 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 
 	static_call(kvm_x86_update_exception_bitmap)(vcpu);
 
+	kvm_arch_vcpu_guestdbg_update_apicv_inhibit(vcpu->kvm);
+
 	r = 0;
 
 out:
-- 
2.26.3