linux-kernel - [PATCH] KVM: X86: expand ->arch.apic_arb

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Date:   Tue, 8 Aug 2017 19:37:14 +0800
From:   "Longpeng(Mike)" <longpeng2@...wei.com>
To:     <pbonzini@...hat.com>, <rkrcmar@...hat.com>
CC:     <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <weidong.huang@...wei.com>, <arei.gonglei@...wei.com>,
        <wangxinxin.wang@...wei.com>, <longpeng.mike@...il.com>,
        "Longpeng(Mike)" <longpeng2@...wei.com>
Subject: [PATCH] KVM: X86: expand ->arch.apic_arb_prio to u64

Currently 'apic_arb_prio' is int32_t, it's too short for long
time running. In our environment, it overflowed and then the
UBSAN was angry:

signed integer overflow:
2147483647 + 1 cannot be represented in type 'int'
CPU: 22 PID: 31237 Comm: qemu-kvm Tainted: ...
...
Call Trace:
 [<ffffffff81f030b6>] dump_stack+0x1e/0x20
 [<ffffffff81f03173>] ubsan_epilogue+0x12/0x55
 [<ffffffff81f04658>] handle_overflow+0x1ba/0x215
 [<ffffffff81f046dd>] __ubsan_handle_add_overflow+0x2a/0x31
 [<ffffffffa126cb1a>] __apic_accept_irq+0x57a/0x5d0 [kvm]
 [<ffffffffa126d14f>] kvm_apic_set_irq+0x9f/0xf0 [kvm]
 [<ffffffffa126db20>] kvm_irq_delivery_to_apic_fast+0x450/0x910 [kvm]
 [<ffffffffa127d8ea>] kvm_irq_delivery_to_apic+0xfa/0x7a0 [kvm]
 [<ffffffffa127e039>] kvm_set_msi+0xa9/0x100 [kvm]
 [<ffffffffa12871ed>] kvm_send_userspace_msi+0x14d/0x1f0 [kvm]
 [<ffffffffa11ed56e>] kvm_vm_ioctl+0x4ee/0xdd0 [kvm]
...

We expand it to u64, this is large enough. Suppose the vcpu receives
1000 irqs per second, then it won't overflow in 584942417 years.
( 18446744073709551615/1000/3600/24/365 = 584942417 )

Signed-off-by: Longpeng(Mike) <longpeng2@...wei.com>
---
 arch/x86/include/asm/kvm_host.h | 2 +-
 arch/x86/kvm/ioapic.h           | 3 ++-
 arch/x86/kvm/irq_comm.c         | 2 +-
 arch/x86/kvm/lapic.c            | 6 +++---
 4 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 87ac4fb..ce9a5f5 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -499,7 +499,7 @@ struct kvm_vcpu_arch {
 	bool apicv_active;
 	DECLARE_BITMAP(ioapic_handled_vectors, 256);
 	unsigned long apic_attention;
-	int32_t apic_arb_prio;
+	u64 apic_arb_prio;
 	int mp_state;
 	u64 ia32_misc_enable_msr;
 	u64 smbase;
diff --git a/arch/x86/kvm/ioapic.h b/arch/x86/kvm/ioapic.h
index 29ce197..a26deed 100644
--- a/arch/x86/kvm/ioapic.h
+++ b/arch/x86/kvm/ioapic.h
@@ -117,7 +117,8 @@ static inline int ioapic_in_kernel(struct kvm *kvm)
 void kvm_rtc_eoi_tracking_restore_one(struct kvm_vcpu *vcpu);
 bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
 		int short_hand, unsigned int dest, int dest_mode);
-int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2);
+/* Return true if vcpu1's priority is lower */
+bool kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2);
 void kvm_ioapic_update_eoi(struct kvm_vcpu *vcpu, int vector,
 			int trigger_mode);
 int kvm_ioapic_init(struct kvm *kvm);
diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
index 3cc3b2d..03b1487 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -90,7 +90,7 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
 			if (!kvm_vector_hashing_enabled()) {
 				if (!lowest)
 					lowest = vcpu;
-				else if (kvm_apic_compare_prio(vcpu, lowest) < 0)
+				else if (kvm_apic_compare_prio(vcpu, lowest))
 					lowest = vcpu;
 			} else {
 				__set_bit(i, dest_vcpu_bitmap);
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 589dcc1..1e2b1f2 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -840,7 +840,7 @@ static inline bool kvm_apic_map_get_dest_lapic(struct kvm *kvm,
 			if (lowest < 0)
 				lowest = i;
 			else if (kvm_apic_compare_prio((*dst)[i]->vcpu,
-						(*dst)[lowest]->vcpu) < 0)
+						(*dst)[lowest]->vcpu))
 				lowest = i;
 		}
 	} else {
@@ -1048,9 +1048,9 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
 	return result;
 }
 
-int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2)
+bool kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2)
 {
-	return vcpu1->arch.apic_arb_prio - vcpu2->arch.apic_arb_prio;
+	return vcpu1->arch.apic_arb_prio < vcpu2->arch.apic_arb_prio;
 }
 
 static bool kvm_ioapic_handles_vector(struct kvm_lapic *apic, int vector)
-- 
1.8.3.1