kvm_get_kvm() kvm_put_kvm() -----Original Message----- From: Nikita Leshenko [mailto:nikita.leshchenko@xxxxxxxxxx] Sent: Tuesday, September 4, 2018 3:57 PM To: Wu, Fengguang <fengguang.wu@xxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>; Linux Memory Management List <linux-mm@xxxxxxxxx>; Peng, DongX <dongx.peng@xxxxxxxxx>; Liu, Jingqi <jingqi.liu@xxxxxxxxx>; Dong, Eddie <eddie.dong@xxxxxxxxx>; Hansen, Dave <dave.hansen@xxxxxxxxx>; Huang, Ying <ying.huang@xxxxxxxxx>; Brendan Gregg <bgregg@xxxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx; LKML <linux-kernel@xxxxxxxxxxxxxxx> Subject: Re: [RFC][PATCH 3/5] [PATCH 3/5] kvm-ept-idle: HVA indexed EPT read On 1 Sep 2018, at 13:28, Fengguang Wu <fengguang.wu@xxxxxxxxx> wrote: > +static ssize_t ept_idle_read(struct file *file, char *buf, > + size_t count, loff_t *ppos) > +{ > + struct task_struct *task = file->private_data; > + struct ept_idle_ctrl *eic; > + unsigned long hva_start = *ppos << BITMAP_BYTE2PVA_SHIFT; > + unsigned long hva_end = hva_start + (count << BITMAP_BYTE2PVA_SHIFT); > + int ret; > + > + if (*ppos % IDLE_BITMAP_CHUNK_SIZE || > + count % IDLE_BITMAP_CHUNK_SIZE) > + return -EINVAL; > + > + eic = kzalloc(sizeof(*eic), GFP_KERNEL); > + if (!eic) > + return -EBUSY; > + > + eic->buf = buf; > + eic->buf_size = count; > + eic->kvm = task_kvm(task); > + if (!eic->kvm) { > + ret = -EINVAL; > + goto out_free; > + } I think you need to increment the refcount while using kvm, otherwise kvm can be destroyed from another thread while you're walking it. -Nikita > + > + ret = ept_idle_walk_hva_range(eic, hva_start, hva_end); > + if (ret) > + goto out_free; > + > + ret = eic->bytes_copied; > + *ppos += ret; > +out_free: > + kfree(eic); > + > + return ret; > +}
