linux-kernel - Re: [PATCH] vfio: remove useless judgement

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Date:   Mon, 27 Jun 2022 16:06:40 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Steve Sistare <steven.sistare@...cle.com>
Cc:     lizhe.67@...edance.com, cohuck@...hat.com, jgg@...pe.ca,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        lizefan.x@...edance.com
Subject: Re: [PATCH] vfio: remove useless judgement


Hey Steve, how did you get around this for cpr or is this a gap?
Thanks,

Alex

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

> From: Li Zhe <lizhe.67@...edance.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@...edance.com>
> Reviewed-by: Jason Gunthorpe <jgg@...pe.ca>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> 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) {