From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 013.lax.mailroute.net (013.lax.mailroute.net [199.89.1.16]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1A1E62DF707 for ; Wed, 25 Mar 2026 21:37:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=199.89.1.16 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774474680; cv=none; b=hCl9vtgzfLwk53zJp3GX+oX9YmVYmLgrfyFo9szg7JBYEInHCVRJFAdkPQkNyTPAmXBw97sUnUA7/yoYpEVwstXwlZO2Ge+jr5dufJ+0vBmwyzhQGimRYYYMZhyZVnza6fc9CUO2fMFMiq6BeY+awp+hcXCnXhL3gKLAndm7/aY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774474680; c=relaxed/simple; bh=9OB6xke2ZbCT8r6Nde15MDC5e/w0yiydX42bwLUPHrs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=K5uE3w4BzOe0rmGJjIP24Z9zGgxm9a8nms0PspmVq38oB21atqetNR/MbdDFl8gcXJIdoi048xMM6nU1kjigh6o0sxV6nOjp4GE3OssNugcUDkOMgtMtOa7h8ANvh5PGIAm1m/HCFqJv1dr8EAGMnAWkP718YSKm80coORo66do= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=acm.org; spf=pass smtp.mailfrom=acm.org; dkim=pass (2048-bit key) header.d=acm.org header.i=@acm.org header.b=tHEOQdyR; arc=none smtp.client-ip=199.89.1.16 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=acm.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=acm.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=acm.org header.i=@acm.org header.b="tHEOQdyR" Received: from localhost (localhost [127.0.0.1]) by 013.lax.mailroute.net (Postfix) with ESMTP id 4fh0d24JChzlfddm; Wed, 25 Mar 2026 21:37:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=acm.org; h= content-transfer-encoding:mime-version:references:in-reply-to :x-mailer:message-id:date:date:subject:subject:from:from :received:received; s=mr01; t=1774474666; x=1777066667; bh=zFlGJ 5Hg/sD1f2lbwWI5MSAAXvxQgejRh5Mze14GvXw=; b=tHEOQdyRboegR9trvoHCk ox+hUuUlvmiZfDOIw+0ZCV7cfgAD+8M04db3uGCFv8N1weHXWglC0Y5R31PRzH02 sX1WYgra3bslm33xtbZer6wJpgE6H6hQt6lL04e9xO3pqvrquYTYRgHu9XHkNfdg gnhF0Ep4+/MrMoFXewVcnvxd+2BzPaXOJcxrJh4JyeeFZd3EYBOOXvv4WK5RGL+J GqXvPJYS19eq7XmSejaawgtBJ7CpJN/qbq/WZrgedMqOrQg5vUpL/38Yp01CmyVR YGSWxduP4onbgfxUqpyn3RI317lK4W7408KLfus5JKKMcmbdp/i8gFnFaaUvxxBn g== X-Virus-Scanned: by MailRoute Received: from 013.lax.mailroute.net ([127.0.0.1]) by localhost (013.lax [127.0.0.1]) (mroute_mailscanner, port 10029) with LMTP id AWqTl2gBGToR; Wed, 25 Mar 2026 21:37:46 +0000 (UTC) Received: from bvanassche.mtv.corp.google.com (unknown [104.135.180.219]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bvanassche@acm.org) by 013.lax.mailroute.net (Postfix) with ESMTPSA id 4fh0ck3370zlfgS0; Wed, 25 Mar 2026 21:37:42 +0000 (UTC) From: Bart Van Assche To: Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Damien Le Moal , Ming Lei , Bart Van Assche , Damien Le Moal , Chaitanya Kulkarni , Keith Busch , Johannes Thumshirn , Genjian Zhang , Hans Holmberg , Thorsten Blum , Nilay Shroff , Kees Cook , "Martin K. Petersen" Subject: [PATCH v2 5/5] null_blk: Support configuring the maximum DMA segment size Date: Wed, 25 Mar 2026 14:37:15 -0700 Message-ID: <20260325213719.2850619-6-bvanassche@acm.org> X-Mailer: git-send-email 2.53.0.1018.g2bb0e51243-goog In-Reply-To: <20260325213719.2850619-1-bvanassche@acm.org> References: <20260325213719.2850619-1-bvanassche@acm.org> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Add support for configuring the maximum DMA segment size. The maximum DMA segment size may be set to a value smaller than the virtual memory page size. No checks are performed on the new max_segment_size parameter because all positive values are valid. The value 0 is converted into a valid value by blk_validate_limits(). Since rq_for_each_segment() may yield bvecs larger than the maximum DMA segment size, add code in the rq_for_each_segment() loop that restricts the bvec length to the maximum DMA segment size. Cc: Christoph Hellwig Cc: Ming Lei Cc: Damien Le Moal Cc: Chaitanya Kulkarni Signed-off-by: Bart Van Assche --- drivers/block/null_blk/main.c | 13 +++++++++++++ drivers/block/null_blk/null_blk.h | 1 + 2 files changed, 14 insertions(+) diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.= c index 677ac829ef80..c43d74cdfd23 100644 --- a/drivers/block/null_blk/main.c +++ b/drivers/block/null_blk/main.c @@ -169,6 +169,10 @@ static int g_max_sectors; module_param_named(max_sectors, g_max_sectors, int, 0444); MODULE_PARM_DESC(max_sectors, "Maximum size of a command (in 512B sector= s)"); =20 +static unsigned int g_max_segment_size =3D BLK_MAX_SEGMENT_SIZE; +module_param_named(max_segment_size, g_max_segment_size, int, 0444); +MODULE_PARM_DESC(max_segment_size, "Maximum size of a DMA segment in byt= es"); + static unsigned int nr_devices =3D 1; module_param(nr_devices, uint, 0444); MODULE_PARM_DESC(nr_devices, "Number of devices to register"); @@ -450,6 +454,7 @@ NULLB_DEVICE_ATTR(home_node, uint, NULL); NULLB_DEVICE_ATTR(queue_mode, uint, NULL); NULLB_DEVICE_ATTR(blocksize, uint, NULL); NULLB_DEVICE_ATTR(max_sectors, uint, NULL); +NULLB_DEVICE_ATTR(max_segment_size, uint, NULL); NULLB_DEVICE_ATTR(irqmode, uint, NULL); NULLB_DEVICE_ATTR(hw_queue_depth, uint, NULL); NULLB_DEVICE_ATTR(index, uint, NULL); @@ -608,6 +613,7 @@ static struct configfs_attribute *nullb_device_attrs[= ] =3D { &nullb_device_attr_index, &nullb_device_attr_irqmode, &nullb_device_attr_max_sectors, + &nullb_device_attr_max_segment_size, &nullb_device_attr_mbps, &nullb_device_attr_memory_backed, &nullb_device_attr_no_sched, @@ -805,6 +811,7 @@ static struct nullb_device *null_alloc_dev(void) dev->queue_mode =3D g_queue_mode; dev->blocksize =3D g_bs; dev->max_sectors =3D g_max_sectors; + dev->max_segment_size =3D g_max_segment_size; dev->irqmode =3D g_irqmode; dev->hw_queue_depth =3D g_hw_queue_depth; dev->blocking =3D g_blocking; @@ -1251,6 +1258,9 @@ static blk_status_t null_transfer(struct nullb *nul= lb, struct page *page, unsigned int valid_len =3D len; void *p; =20 + WARN_ONCE(len > dev->max_segment_size, "%u > %u\n", len, + dev->max_segment_size); + p =3D kmap_local_page(page) + off; if (!is_write) { if (dev->zoned) { @@ -1298,6 +1308,8 @@ static blk_status_t null_handle_data_transfer(struc= t nullb_cmd *cmd, spin_lock_irq(&nullb->lock); rq_for_each_segment(bvec, rq, iter) { len =3D bvec.bv_len; + len =3D min(bvec.bv_len, nullb->dev->max_segment_size); + bvec.bv_len =3D len; if (transferred_bytes + len > max_bytes) len =3D max_bytes - transferred_bytes; err =3D null_transfer(nullb, bvec.bv_page, len, bvec.bv_offset, @@ -1961,6 +1973,7 @@ static int null_add_dev(struct nullb_device *dev) .logical_block_size =3D dev->blocksize, .physical_block_size =3D dev->blocksize, .max_hw_sectors =3D dev->max_sectors, + .max_segment_size =3D dev->max_segment_size, .dma_alignment =3D 1, }; =20 diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/n= ull_blk.h index 6c4c4bbe7dad..43dc47789718 100644 --- a/drivers/block/null_blk/null_blk.h +++ b/drivers/block/null_blk/null_blk.h @@ -93,6 +93,7 @@ struct nullb_device { unsigned int queue_mode; /* block interface */ unsigned int blocksize; /* block size */ unsigned int max_sectors; /* Max sectors per command */ + unsigned int max_segment_size; /* Max size of a single DMA segment. */ unsigned int irqmode; /* IRQ completion handler */ unsigned int hw_queue_depth; /* queue depth */ unsigned int index; /* index of the disk, only valid with a disk */