linux-kernel - Re: [PATCH] misc/genwqe: ensure zero initialization

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Message-Id: <90EFC938-72B5-4D63-84C0-13E3BB2D3184@linux.vnet.ibm.com>
Date:   Thu, 22 Sep 2016 15:19:00 +0200
From:   Frank Haverkamp <haver@...ux.vnet.ibm.com>
To:     Sebastian Ott <sebott@...ux.vnet.ibm.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] misc/genwqe: ensure zero initialization

Hi Sebastian,

> On 12.09.2016, at 20:09, Sebastian Ott <sebott@...ux.vnet.ibm.com> wrote:
> 
> 
> Genwqe uses dma_alloc_coherent and depends on zero initialized memory. On
> one occasion it ueses an explicit memset on others it uses un-initialized
> memory.
> 
> This bug was covered because some archs actually return zero initialized
> memory when using dma_alloc_coherent but this is by no means guaranteed.
> Simply switch to dma_zalloc_coherent.

Thanks for figuring this out. I hope you found all spots where this misassumption is done.

> 
> Signed-off-by: Sebastian Ott <sebott@...ux.vnet.ibm.com>
> ---
> drivers/misc/genwqe/card_ddcb.c  | 2 --
> drivers/misc/genwqe/card_utils.c | 4 ++--
> 2 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/misc/genwqe/card_ddcb.c b/drivers/misc/genwqe/card_ddcb.c
> index 353ee0c..ddfeefe 100644
> --- a/drivers/misc/genwqe/card_ddcb.c
> +++ b/drivers/misc/genwqe/card_ddcb.c
> @@ -1048,8 +1048,6 @@ static int setup_ddcb_queue(struct genwqe_dev *cd, struct ddcb_queue *queue)
> 			"[%s] **err: could not allocate DDCB **\n", __func__);
> 		return -ENOMEM;
> 	}
> -	memset(queue->ddcb_vaddr, 0, queue_size);
> -
> 	queue->ddcb_req = kzalloc(sizeof(struct ddcb_requ *) *
> 				  queue->ddcb_max, GFP_KERNEL);
> 	if (!queue->ddcb_req) {
> diff --git a/drivers/misc/genwqe/card_utils.c b/drivers/misc/genwqe/card_utils.c
> index 222367c..8a679ec 100644
> --- a/drivers/misc/genwqe/card_utils.c
> +++ b/drivers/misc/genwqe/card_utils.c
> @@ -220,8 +220,8 @@ void *__genwqe_alloc_consistent(struct genwqe_dev *cd, size_t size,
> 	if (get_order(size) > MAX_ORDER)
> 		return NULL;
> 
> -	return dma_alloc_coherent(&cd->pci_dev->dev, size, dma_handle,
> -				  GFP_KERNEL);
> +	return dma_zalloc_coherent(&cd->pci_dev->dev, size, dma_handle,
> +				   GFP_KERNEL);
> }
> 
> void __genwqe_free_consistent(struct genwqe_dev *cd, size_t size,
> -- 
> 2.5.5
> 
I think this should be fine.

Signed-off-by: Frank Haverkamp <haver@...ux.vnet.ibm.com>