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Subject: Re: [RFC PATCH] vfio: type1: fix kthread use case
To:     Hillf Danton <hdanton@sina.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        iommu@lists.linux-foundation.org
Cc:     kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org,
        Christoph Hellwig <hch@lst.de>,
        =?UTF-8?B?SsO2cmcgUsO2ZGVs?= <joro@8bytes.org>,
        Kevin Tian <kevin.tian@intel.com>,
        Yan Zhao <yan.y.zhao@intel.com>
References: <20200706104915.11460-1-hdanton@sina.com>
 <20200706124241.4392-1-hdanton@sina.com>
From:   Markus Elfring <Markus.Elfring@web.de>
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Date:   Mon, 6 Jul 2020 16:04:13 +0200
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=E2=80=A6
> +++ b/drivers/vfio/vfio_iommu_type1.c
=E2=80=A6
> @@ -2812,11 +2815,10 @@ static int vfio_iommu_type1_dma_rw_chunk
=E2=80=A6
>  	if (!mm)
>  		return -EPERM;
>
> -	if (kthread)
> +	if (kthread && use_mm)

Can another design approach make sense here?

+	bool thread_use_mm =3D ((current->flags & PF_KTHREAD) && !current->mm);
+	if (thread_use_mm)


>  		kthread_use_mm(mm);
=E2=80=A6

Regards,
Markus