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Date: Tue, 4 Sep 2018 16:15:05 +0800
From: Fengguang Wu <fengguang.wu@intel.com>
Subject: Re: [RFC][PATCH 3/5] [PATCH 3/5] kvm-ept-idle: HVA indexed EPT read
Message-ID: <20180904081505.4vu4rx6ksdnp5nk4@wfg-t540p.sh.intel.com>
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 <20180901124811.591511876@intel.com>
 <37B30FD3-7955-4C0B-AAB5-544359F4D157@oracle.com>
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To: "Peng, DongX" <dongx.peng@intel.com>
Cc: Nikita Leshenko <nikita.leshchenko@oracle.com>, Andrew Morton <akpm@linux-foundation.org>, Linux Memory Management List <linux-mm@kvack.org>, "Liu, Jingqi" <jingqi.liu@intel.com>, "Dong, Eddie" <eddie.dong@intel.com>, "Hansen, Dave" <dave.hansen@intel.com>, "Huang, Ying" <ying.huang@intel.com>, Brendan Gregg <bgregg@netflix.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>

Yeah thanks! Currently we are restructuring the related functions,
will add these calls when sorted out the walk order and hole issues.

Thanks,
Fengguang

On Tue, Sep 04, 2018 at 04:12:00PM +0800, Peng Dong wrote:
>kvm_get_kvm() kvm_put_kvm()
>
>-----Original Message-----
>From: Nikita Leshenko [mailto:nikita.leshchenko@oracle.com]
>Sent: Tuesday, September 4, 2018 3:57 PM
>To: Wu, Fengguang <fengguang.wu@intel.com>
>Cc: Andrew Morton <akpm@linux-foundation.org>; Linux Memory Management List <linux-mm@kvack.org>; Peng, DongX <dongx.peng@intel.com>; Liu, Jingqi <jingqi.liu@intel.com>; Dong, Eddie <eddie.dong@intel.com>; Hansen, Dave <dave.hansen@intel.com>; Huang, Ying <ying.huang@intel.com>; Brendan Gregg <bgregg@netflix.com>; kvm@vger.kernel.org; LKML <linux-kernel@vger.kernel.org>
>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@intel.com> 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;
>> +}
>