linux-kernel - Re: [PATCH 2/2] xen/gntdev: Fix partial gntdev

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Message-ID: <e2686907-2715-15e8-4cdf-3165903db3ee@oracle.com>
Date:   Tue, 9 Jan 2018 20:22:56 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Ross Lagerwall <ross.lagerwall@...rix.com>,
        xen-devel@...ts.xenproject.org
Cc:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] xen/gntdev: Fix partial gntdev_mmap() cleanup



On 01/09/2018 07:10 AM, Ross Lagerwall wrote:
> When cleaning up after a partially successful gntdev_mmap(), unmap the
> successfully mapped grant pages otherwise Xen will kill the domain if
> in debug mode (Attempt to implicitly unmap a granted PTE) or Linux will
> kill the process and emit "BUG: Bad page map in process" if Xen is in
> release mode.
> 
> This is only needed when use_ptemod is true because gntdev_put_map()
> will unmap grant pages itself when use_ptemod is false.
> 
> Signed-off-by: Ross Lagerwall <ross.lagerwall@...rix.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>

although I wonder whether it may be possible to have gntdev_put_map() 
figure whether to unmap the pages if use_ptemod is set.

> ---
>   drivers/xen/gntdev.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index d3391a1..bd56653 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -1071,8 +1071,10 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>   out_unlock_put:
>   	mutex_unlock(&priv->lock);
>   out_put_map:
> -	if (use_ptemod)
> +	if (use_ptemod) {
>   		map->vma = NULL;
> +		unmap_grant_pages(map, 0, map->count);
> +	}
>   	gntdev_put_map(priv, map);
>   	return err;
>   }
>