Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 30 Jun 2022 13:51:40 -0600
From:   Alex Williamson <alex.williamson@redhat.com>
To:     lizhe.67@bytedance.com
Cc:     cohuck@redhat.com, jgg@ziepe.ca, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, lizefan.x@bytedance.com
Subject: Re: [PATCH] vfio: remove useless judgement
Message-ID: <20220630135140.5069b23c.alex.williamson@redhat.com>
In-Reply-To: <20220627035109.73745-1-lizhe.67@bytedance.com>
References: <20220627035109.73745-1-lizhe.67@bytedance.com>
Organization: Red Hat
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Precedence: bulk

On Mon, 27 Jun 2022 11:51:09 +0800
lizhe.67@bytedance.com wrote:

> From: Li Zhe <lizhe.67@bytedance.com>
> 
> In function vfio_dma_do_unmap(), we currently prevent process to unmap
> vfio dma region whose mm_struct is different from the vfio_dma->task.
> In our virtual machine scenario which is using kvm and qemu, this
> judgement stops us from liveupgrading our qemu, which uses fork() &&
> exec() to load the new binary but the new process cannot do the
> VFIO_IOMMU_UNMAP_DMA action during vm exit because of this judgement.
> 
> This judgement is added in commit 8f0d5bb95f76 ("vfio iommu type1: Add
> task structure to vfio_dma") for the security reason. But it seems that
> no other task who has no family relationship with old and new process
> can get the same vfio_dma struct here for the reason of resource
> isolation. So this patch delete it.
> 
> Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
> Reviewed-by: Jason Gunthorpe <jgg@ziepe.ca>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 6 ------
>  1 file changed, 6 deletions(-)

Applied to vfio next branch for v5.20.  Thanks,

Alex

> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index c13b9290e357..a8ff00dad834 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -1377,12 +1377,6 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>  
>  		if (!iommu->v2 && iova > dma->iova)
>  			break;
> -		/*
> -		 * Task with same address space who mapped this iova range is
> -		 * allowed to unmap the iova range.
> -		 */
> -		if (dma->task->mm != current->mm)
> -			break;
>  
>  		if (invalidate_vaddr) {
>  			if (dma->vaddr_invalid) {