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From: Boris Pismenny <borispismenny@gmail.com>
To: Christoph Hellwig <hch@infradead.org>,
	Boris Pismenny <borisp@nvidia.com>
Cc: dsahern@gmail.com, kuba@kernel.org, davem@davemloft.net,
	saeedm@nvidia.com, hch@lst.de, sagi@grimberg.me, axboe@fb.com,
	kbusch@kernel.org, viro@zeniv.linux.org.uk, edumazet@google.com,
	smalin@marvell.com, boris.pismenny@gmail.com,
	linux-nvme@lists.infradead.org, netdev@vger.kernel.org,
	benishay@nvidia.com, ogerlitz@nvidia.com, yorayz@nvidia.com,
	Boris Pismenny <borisp@mellanox.com>,
	Ben Ben-Ishay <benishay@mellanox.com>,
	Or Gerlitz <ogerlitz@mellanox.com>,
	Yoray Zack <yorayz@mellanox.com>
Subject: Re: [PATCH v5 net-next 02/36] iov_iter: DDP copy to iter/pages
Date: Thu, 22 Jul 2021 23:23:38 +0300	[thread overview]
Message-ID: <6f7f96dc-f1e6-99d9-6ab4-920126615302@gmail.com> (raw)
In-Reply-To: <YPlzHTnoxDinpOsP@infradead.org>

On 22/07/2021 16:31, Christoph Hellwig wrote:
>> +#ifdef CONFIG_ULP_DDP
>> +size_t _ddp_copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
>> +#endif
>>  size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i);
>>  bool _copy_from_iter_full(void *addr, size_t bytes, struct iov_iter *i);
>>  size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i);
>> @@ -145,6 +148,16 @@ size_t copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
>>  		return _copy_to_iter(addr, bytes, i);
>>  }
>>  
>> +#ifdef CONFIG_ULP_DDP
>> +static __always_inline __must_check
>> +size_t ddp_copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
>> +{
>> +	if (unlikely(!check_copy_size(addr, bytes, true)))
>> +		return 0;
>> +	return _ddp_copy_to_iter(addr, bytes, i);
>> +}
>> +#endif
> 
> There is no need to ifdef out externs with conditional implementations,
> or inlines using them.
> 
>> +#ifdef CONFIG_ULP_DDP
>> +static void ddp_memcpy_to_page(struct page *page, size_t offset, const char *from, size_t len)
> 
> Overly long line.
> 
>> +	char *to = kmap_atomic(page);
>> +
>> +	if (to + offset != from)
>> +		memcpy(to + offset, from, len);
>> +
>> +	kunmap_atomic(to);
> 
> This looks completely bogus to any casual read, so please document why
> it makes sense.  And no, a magic, unexplained ddp in the name does not
> count as explanation at all.  Please think about a more useful name.

This routine, like other changes in this file, replicates the logic in
memcpy_to_page. The only difference is that "ddp" avoids copies when the
copy source and destinations buffers are one and the same. These are
then used by nvme-tcp (see skb_ddp_copy_datagram_iter in nvme-tcp) which
receives SKBs from the NIC that already placed data in its destination,
and this is the source for the name Direct Data Placement. I'd gladly
take suggestions for better names, but this is the best we came up with
so far.

The reason we are doing it is to avoid modifying memcpy_to_page itself,
but rather allow users (e.g., nvme-tcp) to access this functionality
directly.

> 
> Can this ever write to user page?  If yes it needs a flush_dcache_page.

Yes, will add.

> 
> Last but not least: kmap_atomic is deprecated except for the very
> rate use case where it is actually called from atomic context.  Please
> use kmap_local_page instead.
> 

Will look into it, thanks!

>> +#ifdef CONFIG_CRYPTO_HASH
>> +	struct ahash_request *hash = hashp;
>> +	struct scatterlist sg;
>> +	size_t copied;
>> +
>> +	copied = ddp_copy_to_iter(addr, bytes, i);
>> +	sg_init_one(&sg, addr, copied);
>> +	ahash_request_set_crypt(hash, &sg, NULL, copied);
>> +	crypto_ahash_update(hash);
>> +	return copied;
>> +#else
>> +	return 0;
>> +#endif
> 
> What is the point of this stub?  To me it looks extremely dangerous.
> 

As above, we use the same logic as in hash_and_copy_to_iter. The purpose
is again to eventually avoid the copy in case the source and destination
buffers are one and the same.

  reply	other threads:[~2021-07-22 20:23 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-22 11:02 [PATCH v5 net-next 00/36] nvme-tcp receive and tarnsmit offloads Boris Pismenny
2021-07-22 11:02 ` [PATCH v5 net-next 01/36] net: Introduce direct data placement tcp offload Boris Pismenny
2021-07-22 11:26   ` Eric Dumazet
2021-07-22 12:18     ` Boris Pismenny
2021-07-22 13:10       ` Eric Dumazet
2021-07-22 13:33         ` Boris Pismenny
2021-07-22 13:39           ` Eric Dumazet
2021-07-22 14:02             ` Boris Pismenny
2021-07-22 11:02 ` [PATCH v5 net-next 02/36] iov_iter: DDP copy to iter/pages Boris Pismenny
2021-07-22 13:31   ` Christoph Hellwig
2021-07-22 20:23     ` Boris Pismenny [this message]
2021-07-23  5:03       ` Christoph Hellwig
2021-07-23  5:21         ` Al Viro
2021-08-04 14:13           ` Or Gerlitz
2021-08-10 13:29             ` Or Gerlitz
2021-07-22 20:55   ` Al Viro
2021-07-22 11:02 ` [PATCH v5 net-next 03/36] net: skb copy(+hash) iterators for DDP offloads Boris Pismenny
2021-07-22 11:02 ` [PATCH v5 net-next 04/36] net/tls: expose get_netdev_for_sock Boris Pismenny
2021-07-23  6:06   ` Christoph Hellwig
2021-08-04 13:26     ` Or Gerlitz
     [not found]       ` <20210804072918.17ba9cff@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
2021-08-04 15:07         ` Or Gerlitz
2021-08-10 13:25           ` Or Gerlitz
2021-07-22 11:02 ` [PATCH v5 net-next 05/36] nvme-tcp: Add DDP offload control path Boris Pismenny
2021-07-22 11:02 ` [PATCH v5 net-next 06/36] nvme-tcp: Add DDP data-path Boris Pismenny
2021-07-22 11:02 ` [PATCH v5 net-next 07/36] nvme-tcp: RX DDGST offload Boris Pismenny
2021-07-22 11:02 ` [PATCH v5 net-next 08/36] nvme-tcp: Deal with netdevice DOWN events Boris Pismenny
2021-07-22 11:02 ` [PATCH v5 net-next 09/36] net/mlx5: Header file changes for nvme-tcp offload Boris Pismenny
2021-07-22 11:02 ` [PATCH v5 net-next 10/36] net/mlx5: Add 128B CQE for NVMEoTCP offload Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 11/36] net/mlx5e: TCP flow steering for nvme-tcp Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 12/36] net/mlx5e: NVMEoTCP offload initialization Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 13/36] net/mlx5e: KLM UMR helper macros Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 14/36] net/mlx5e: NVMEoTCP use KLM UMRs Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 15/36] net/mlx5e: NVMEoTCP queue init/teardown Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 16/36] net/mlx5e: NVMEoTCP async ddp invalidation Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 17/36] net/mlx5e: NVMEoTCP ddp setup and resync Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 18/36] net/mlx5e: NVMEoTCP, data-path for DDP+DDGST offload Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 19/36] net/mlx5e: NVMEoTCP statistics Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 20/36] Documentation: add ULP DDP offload documentation Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 21/36] net: drop ULP DDP HW offload feature if no CSUM offload feature Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 22/36] net: Add ulp_ddp_pdu_info struct Boris Pismenny
2021-07-23 19:42   ` Sagi Grimberg
2021-07-22 11:03 ` [PATCH v5 net-next 23/36] net: Add to ulp_ddp support for fallback flow Boris Pismenny
2021-07-23  6:09   ` Christoph Hellwig
2021-07-22 11:03 ` [PATCH v5 net-next 24/36] net: Add MSG_DDP_CRC flag Boris Pismenny
2021-07-22 14:23   ` Eric Dumazet
2021-07-22 11:03 ` [PATCH v5 net-next 25/36] nvme-tcp: TX DDGST offload Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 26/36] nvme-tcp: Mapping between Tx NVMEoTCP pdu and TCP sequence Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 27/36] mlx5e: make preparation in TLS code for NVMEoTCP CRC Tx offload Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 28/36] mlx5: Add sq state test bit for nvmeotcp Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 29/36] mlx5: Add support to NETIF_F_HW_TCP_DDP_CRC_TX feature Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 30/36] net/mlx5e: NVMEoTCP DDGST TX offload TIS Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 31/36] net/mlx5e: NVMEoTCP DDGST Tx offload queue init/teardown Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 32/36] net/mlx5e: NVMEoTCP DDGST TX BSF and PSV Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 33/36] net/mlx5e: NVMEoTCP DDGST TX Data path Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 34/36] net/mlx5e: NVMEoTCP DDGST TX handle OOO packets Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 35/36] net/mlx5e: NVMEoTCP DDGST TX offload optimization Boris Pismenny
2021-07-22 11:03 ` [PATCH v5 net-next 36/36] net/mlx5e: NVMEoTCP DDGST TX statistics Boris Pismenny
2021-07-23  5:56 ` [PATCH v5 net-next 00/36] nvme-tcp receive and tarnsmit offloads Christoph Hellwig
2021-07-23 19:58   ` Sagi Grimberg
2021-08-04 13:51     ` Or Gerlitz
2021-08-06 19:46       ` Sagi Grimberg
2021-08-10 13:37         ` Or Gerlitz

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