KVM: lapic: fix access preemption timer stuff even if kernel_irqchip=off

Wanpeng Li · bonzini · commit 910053002ef1 · 2016-08-04T14:21:43.000+02:00
BUG: unable to handle kernel NULL pointer dereference at 000000000000008c
IP: [&lt;ffffffffc04e0180&gt;] kvm_lapic_hv_timer_in_use+0x10/0x20 [kvm]
PGD 0
Oops: 0000 [#1] SMP
Call Trace:
 kvm_arch_vcpu_load+0x86/0x260 [kvm]
 vcpu_load+0x46/0x60 [kvm]
 kvm_vcpu_ioctl+0x79/0x7c0 [kvm]
 ? __lock_is_held+0x54/0x70
 do_vfs_ioctl+0x96/0x6a0
 ? __fget_light+0x2a/0x90
 SyS_ioctl+0x79/0x90
 do_syscall_64+0x7c/0x1e0
 entry_SYSCALL64_slow_path+0x25/0x25
RIP  [&lt;ffffffffc04e0180&gt;] kvm_lapic_hv_timer_in_use+0x10/0x20 [kvm]
 RSP &lt;ffff8800db1f3d70&gt;
CR2: 000000000000008c
---[ end trace a55fb79d2b3b4ee8 ]---

This can be reproduced steadily by kernel_irqchip=off.

We should not access preemption timer stuff if lapic is emulated in userspace.
This patch fix it by avoiding access preemption timer stuff when kernel_irqchip=off.

Cc: Paolo Bonzini &lt;pbonzini@redhat.com&gt;
Cc: Radim Krčmář &lt;rkrcmar@redhat.com&gt;
Cc: Yunhong Jiang &lt;yunhong.jiang@intel.com&gt;
Signed-off-by: Wanpeng Li &lt;wanpeng.li@hotmail.com&gt;
Signed-off-by: Paolo Bonzini &lt;pbonzini@redhat.com&gt;
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
@@ -1349,6 +1349,9 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic)
 
 bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu)
 {
+	if (!lapic_in_kernel(vcpu))
+		return false;
+
 	return vcpu->arch.apic->lapic_timer.hv_timer_in_use;
 }
 EXPORT_SYMBOL_GPL(kvm_lapic_hv_timer_in_use);

Original file line number	Diff line number	Diff line change
`@@ -1349,6 +1349,9 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic)`
`1349`	`1349`
`1350`	`1350`	`bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu)`
`1351`	`1351`	`{`
	`1352`	`+ if (!lapic_in_kernel(vcpu))`
	`1353`	`+ return false;`
	`1354`	`+`
`1352`	`1355`	`return vcpu->arch.apic->lapic_timer.hv_timer_in_use;`
`1353`	`1356`	`}`
`1354`	`1357`	`EXPORT_SYMBOL_GPL(kvm_lapic_hv_timer_in_use);`