linux-kernel - Re: [PATCH 5.10 04/57] net: octeontx2: Make sure the buffer is 128 byte aligned

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Message-ID: <20210207092015.GA32297@amd>
Date:   Sun, 7 Feb 2021 10:20:15 +0100
From:   Pavel Machek <pavel@....cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Subbaraya Sundeep <sbhatta@...vell.com>,
        Kevin Hao <haokexin@...il.com>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH 5.10 04/57] net: octeontx2: Make sure the buffer is 128
 byte aligned

Hi!

> commit db2805150a0f27c00ad286a29109397a7723adad upstream.
> 
> The octeontx2 hardware needs the buffer to be 128 byte aligned.
> But in the current implementation of napi_alloc_frag(), it can't
> guarantee the return address is 128 byte aligned even the request size
> is a multiple of 128 bytes, so we have to request an extra 128 bytes and
> use the PTR_ALIGN() to make sure that the buffer is aligned correctly.
> 
> +++ b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
> @@ -473,10 +473,11 @@ dma_addr_t __otx2_alloc_rbuf(struct otx2
>  	dma_addr_t iova;
>  	u8 *buf;
>  
> -	buf = napi_alloc_frag(pool->rbsize);
> +	buf = napi_alloc_frag(pool->rbsize + OTX2_ALIGN);
>  	if (unlikely(!buf))
>  		return -ENOMEM;
>  
> +	buf = PTR_ALIGN(buf, OTX2_ALIGN);

So we allocate a buffer, then change it, and then pass modified
pointer to the page_frag_free(buf); in the error path. That... can't
be right, right?

>  	iova = dma_map_single_attrs(pfvf->dev, buf, pool->rbsize,
>  				    DMA_FROM_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
>  	if (unlikely(dma_mapping_error(pfvf->dev, iova))) {

BTW otx2_alloc_rbuf and __otx2_alloc_rbuf should probably return s64,
as they return negative error code...

Best regards,
							Pavel

-- 
http://www.livejournal.com/~pavelmachek

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