netdev - Re: Regression bisected to "crypto: af_alg: Convert af_alg_sendpage() to use MSG_SPLICE

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Message-ID: <1506614.1688481248@warthog.procyon.org.uk>
Date: Tue, 04 Jul 2023 15:34:08 +0100
From: David Howells <dhowells@...hat.com>
To: Ondrej Mosnáček <omosnacek@...il.com>
Cc: dhowells@...hat.com,
    Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
    Herbert Xu <herbert@...dor.apana.org.au>,
    Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Subject: Re: Regression bisected to "crypto: af_alg: Convert af_alg_sendpage() to use MSG_SPLICE_PAGES"

The problem is caused by this bit in af_alg_sendmsg():

		/* use the existing memory in an allocated page */
		if (ctx->merge) {
			sgl = list_entry(ctx->tsgl_list.prev,
					 struct af_alg_tsgl, list);
			sg = sgl->sg + sgl->cur - 1;
			len = min_t(size_t, len,
				    PAGE_SIZE - sg->offset - sg->length);

			err = memcpy_from_msg(page_address(sg_page(sg)) +
					      sg->offset + sg->length,
					      msg, len);
			if (err)
				goto unlock;

			sg->length += len;
			ctx->merge = (sg->offset + sg->length) &
				     (PAGE_SIZE - 1);

			ctx->used += len;
			copied += len;
			size -= len;
			continue;
		}

it doesn't exist in the old af_alg_sendpage() code.  It merges data supplied
by sendmsg() into the last page in the list if there's space.  So we need a
flag to keep track of whether the last page is appendable-to or not.

David