netdev - RE: [PATCH] net: octeontx2: Make sure the buffer is 128 byte aligned

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Date:   Thu, 21 Jan 2021 09:53:08 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kevin Hao' <haokexin@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Subbaraya Sundeep <sbhatta@...vell.com>
CC:     Sunil Goutham <sgoutham@...vell.com>,
        Geetha sowjanya <gakula@...vell.com>,
        hariprasad <hkelam@...vell.com>
Subject: RE: [PATCH] net: octeontx2: Make sure the buffer is 128 byte aligned

From: Kevin Hao
> Sent: 21 January 2021 07:09
> 
> 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.
> 
> Fixes: 7a36e4918e30 ("octeontx2-pf: Use the napi_alloc_frag() to alloc the pool buffers")
> Reported-by: Subbaraya Sundeep <sbhatta@...vell.com>
> Signed-off-by: Kevin Hao <haokexin@...il.com>
> ---
>  drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
> b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
> index bdfa2e293531..5ddedc3b754d 100644
> --- a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
> +++ b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
> @@ -488,10 +488,11 @@ dma_addr_t __otx2_alloc_rbuf(struct otx2_nic *pfvf, struct otx2_pool *pool)
>  	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);
>  	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))) {
> --
> 2.29.2

Doesn't that break the 'free' code ?
Surely it needs the original pointer.

It isn't obvious that page_frag_free() it correct when the
allocator is napi_alloc_frag() either.
I'd have thought it ought to be returned to the pool.

	David

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