On 20/11/2017 10:17, Wanpeng Li wrote: > ------------[ cut here ]------------ > WARNING: CPU: 6 PID: 24431 at /home/kernel/linux/arch/x86/kvm//x86.c:7302 kvm_arch_vcpu_ioctl_run+0x651/0x2ea0 [kvm] > CPU: 6 PID: 24431 Comm: reprotest Tainted: G W OE 4.14.0+ #26 > RIP: 0010:kvm_arch_vcpu_ioctl_run+0x651/0x2ea0 [kvm] > RSP: 0018:ffff880291d179e0 EFLAGS: 00010202 > Call Trace: > ? synchronize_rcu.part.59+0x9b/0xf0 > ? synchronize_rcu_expedited+0xa0/0xa0 > ? kfree_call_rcu+0x20/0x20 > ? trace_raw_output_rcu_utilization+0x70/0x70 > ? kvm_arch_vcpu_runnable+0x220/0x220 [kvm] > ? wait_for_completion+0x222/0x2a0 > ? __wait_rcu_gp+0x1d3/0x230 > ? kvm_vcpu_ioctl+0x479/0x880 [kvm] > kvm_vcpu_ioctl+0x479/0x880 [kvm] > ? kvm_dev_ioctl+0xba0/0xba0 [kvm] > ? pick_next_task_fair+0x629/0xce0 > ? sched_clock+0x1b/0x20 > ? check_chain_key+0x131/0x1e0 > ? lock_acquire+0x2c0/0x2c0 > ? check_flags.part.44+0x62/0x250 > ? check_chain_key+0x131/0x1e0 > ? __lock_acquire+0xd2e/0x1cb0 > do_vfs_ioctl+0x142/0x9a0 > ? ioctl_preallocate+0x150/0x150 > ? lock_acquire+0x2c0/0x2c0 > ? lock_acquire+0x118/0x2c0 > ? __lock_is_held+0x4b/0xe0 > ? __fget+0x16a/0x250 > SyS_ioctl+0x74/0x80 > entry_SYSCALL_64_fastpath+0x23/0x9a Please leave out the "?" lines of the backtrace, and if possible include the C code for the testcase. > The syzkaller testcase tries to setup the processor specific debug registers > and configure vCPU for handling guest debug events through KVM_SET_GUEST_DEBUG. > The KVM_SET_GUEST_DEBUG ioctl will get and set rflags in order to set TF bit > if single step is needed. All regs' caches are reset to avail and GUEST_RFLAGS > vmcs field is reset to 0x2 during vCPU reset. However, the cache of rflags is > not reset during vCPU reset. The function vmx_get_rflags() returns an unreset > rflags cache value since the cache is marked avail, it is 0 after boot. Vmentry > fails if the rflags reserved bit 1 is 0. > > This patch fixes it by resetting both the GUEST_RFLAGS vmcs field and its cache > to 0x2 during vCPU reset. > > Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> > Cc: Nadav Amit <nadav.amit@xxxxxxxxx> > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > --- > arch/x86/kvm/vmx.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index b348920..131fa1c 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -5590,6 +5590,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) > vmcs_write64(GUEST_IA32_DEBUGCTL, 0); > } > > + vmx->rflags = 0x02; > vmcs_writel(GUEST_RFLAGS, 0x02); > kvm_rip_write(vcpu, 0xfff0); > > Maybe this should be just kvm_set_rflags(vcpu, 2); just like in svm.c's init_vmcb? Thanks, Paolo
