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Date:   Tue, 24 Oct 2017 14:33:53 -0700
From:   Omar Sandoval <osandov@...ndov.com>
To:     Jens Axboe <axboe@...com>, Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:     linux-kernel@...r.kernel.org, hch@....de,
        Nishita Borkar <nishita.borkar@...cle.com>,
        linux-block@...r.kernel.org
Subject: Re: [PATCH] block: Invalidate cache on discard v2

On Wed, Mar 22, 2017 at 11:29:25PM +0400, Dmitry Monakhov wrote:
> It is reasonable drop page cache on discard, otherwise that pages may
> be written by writeback second later, so thin provision devices will
> not be happy. This seems to be a  security leak in case of secure discard case.
> 
> Also add check for queue_discard flag on early stage.
> 
> Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
> Reviewed-by: Christoph Hellwig <hch@....de>
> 
> ---
>  block/ioctl.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/block/ioctl.c b/block/ioctl.c
> index 7b88820..336610d 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -202,10 +202,16 @@ static int blk_ioctl_discard(struct block_device *bdev, fmode_t mode,
>  {
>  	uint64_t range[2];
>  	uint64_t start, len;
> +	struct request_queue *q = bdev_get_queue(bdev);
> +	struct address_space *mapping = bdev->bd_inode->i_mapping;
> +
>  
>  	if (!(mode & FMODE_WRITE))
>  		return -EBADF;
>  
> +	if (!blk_queue_discard(q))
> +		return -EOPNOTSUPP;
> +
>  	if (copy_from_user(range, (void __user *)arg, sizeof(range)))
>  		return -EFAULT;
>  
> @@ -216,12 +222,12 @@ static int blk_ioctl_discard(struct block_device *bdev, fmode_t mode,
>  		return -EINVAL;
>  	if (len & 511)
>  		return -EINVAL;
> -	start >>= 9;
> -	len >>= 9;
>  
> -	if (start + len > (i_size_read(bdev->bd_inode) >> 9))
> +	if (start + len > i_size_read(bdev->bd_inode))
>  		return -EINVAL;
> -	return blkdev_issue_discard(bdev, start, len, GFP_KERNEL, flags);
> +	truncate_inode_pages_range(mapping, start, start + len);
> +	return blkdev_issue_discard(bdev, start >> 9, len >> 9,
> +				    GFP_KERNEL, flags);
>  }
>  
>  static int blk_ioctl_zeroout(struct block_device *bdev, fmode_t mode,
> -- 
> 2.9.3
> 

Hey, Jens, Dmitry didn't send this patch to linux-block so looks like
you missed it. Christoph reviewed it and Nishita sent up a blktest for
it so we should probably pull it in.

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