linux-kernel - Re: [PATCH 1/2] KVM: lapic: fix access preemption timer stuff even if kernel

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Date:	Wed, 3 Aug 2016 18:03:53 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Radim Krčmář <rkrcmar@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, Wanpeng Li <wanpeng.li@...mail.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Yunhong Jiang <yunhong.jiang@...el.com>
Subject: Re: [PATCH 1/2] KVM: lapic: fix access preemption timer stuff even if kernel_irqchip=off

2016-08-03 17:55 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> 2016-08-03 12:04+0800, Wanpeng Li:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> BUG: unable to handle kernel NULL pointer dereference at 000000000000008c
>> IP: [<ffffffffc04e0180>] 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  [<ffffffffc04e0180>] kvm_lapic_hv_timer_in_use+0x10/0x20 [kvm]
>>  RSP <ffff8800db1f3d70>
>> 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 <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: Yunhong Jiang <yunhong.jiang@...el.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>
> Reviewed-by: Radim Krčmář <rkrcmar@...hat.com>
>
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> @@ -1348,6 +1348,9 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic)
>>
>>  bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu)
>
> Btw, the "hv" in makes it look like it has something to do with Hyper-V.
> What does "hv" stand for anyway?  Hardware Virtualized?

Hmm, yeah, hv_timer make people confusing.
http://www.spinics.net/lists/kvm/msg134205.html

Regards,
Wanpeng Li