Re: [PATCH v5 net-next 02/36] iov_iter: DDP copy to iter/pages

[Christoph Hellwig <hch@infradead.org>]

> +#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.

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

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.

> +#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.