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Date:   Tue, 25 Jul 2023 11:16:59 +0530
From:   Pavan Kondeti <quic_pkondeti@quicinc.com>
To:     Mike Tipton <quic_mdtipton@quicinc.com>
CC:     <djakov@kernel.org>, <gregkh@linuxfoundation.org>,
        <rafael@kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-pm@vger.kernel.org>, <quic_okukatla@quicinc.com>,
        <quic_viveka@quicinc.com>
Subject: Re: [PATCH 3/3] interconnect: Add debugfs test client
Message-ID: <0a596a36-7ff6-445e-9052-c86623130bd9@quicinc.com>
References: <20230725012859.18474-1-quic_mdtipton@quicinc.com>
 <20230725012859.18474-4-quic_mdtipton@quicinc.com>
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In-Reply-To: <20230725012859.18474-4-quic_mdtipton@quicinc.com>
Precedence: bulk

On Mon, Jul 24, 2023 at 06:28:59PM -0700, Mike Tipton wrote:
> It's often useful during test, debug, and development to issue path
> votes from shell. Add a debugfs client for this purpose.
> 
> Example usage:
> 	cd /sys/kernel/debug/interconnect/test-client/
> 
> 	# Configure node endpoints for the path from CPU to DDR on
> 	# qcom/sm8550.
> 	echo chm_apps > src_node
> 	echo ebi > dst_node
> 
> 	# Get path between src_node and dst_node. This is only
> 	# necessary after updating the node endpoints.
> 	echo 1 > get
> 
> 	# Set desired BW to 1GBps avg and 2GBps peak.
> 	echo 1000000 > avg_bw
> 	echo 2000000 > peak_bw
> 
> 	# Vote for avg_bw and peak_bw on the latest path from "get".
> 	# Voting for multiple paths is possible by repeating this
> 	# process for different nodes endpoints.
> 	echo 1 > commit
> 

Can Documentation/driver-api/interconnect.rst be updated with this
information?

> Allowing userspace to directly enable and set bus rates can be dangerous
> So, following in the footsteps of the regmap [0] and clk [1] frameworks,
> keep these userspace controls compile-time disabled without Kconfig
> options to enable them. Enabling this will require code changes to
> define INTERCONNECT_ALLOW_WRITE_DEBUGFS.
>  

Completely agree with your argument here.

> [0] commit 09c6ecd39410 ("regmap: Add support for writing to regmap registers via debugfs")
> [1] commit 37215da5553e ("clk: Add support for setting clk_rate via debugfs")
> 
> Signed-off-by: Mike Tipton <quic_mdtipton@quicinc.com>
> ---
>  drivers/interconnect/Makefile         |   2 +-
>  drivers/interconnect/core.c           |   3 +
>  drivers/interconnect/debugfs-client.c | 156 ++++++++++++++++++++++++++
>  drivers/interconnect/internal.h       |   2 +
>  4 files changed, 162 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/interconnect/debugfs-client.c
> 
> diff --git a/drivers/interconnect/Makefile b/drivers/interconnect/Makefile
> index 5604ce351a9f..d0888babb9a1 100644
> --- a/drivers/interconnect/Makefile
> +++ b/drivers/interconnect/Makefile
> @@ -1,7 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
>  CFLAGS_core.o				:= -I$(src)
> -icc-core-objs				:= core.o bulk.o
> +icc-core-objs				:= core.o bulk.o debugfs-client.o
>  
>  obj-$(CONFIG_INTERCONNECT)		+= icc-core.o
>  obj-$(CONFIG_INTERCONNECT_IMX)		+= imx/
> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> index 511152398790..bc82571ff2a8 100644
> --- a/drivers/interconnect/core.c
> +++ b/drivers/interconnect/core.c
> @@ -1117,6 +1117,9 @@ static int __init icc_init(void)
>  			    icc_debugfs_dir, NULL, &icc_summary_fops);
>  	debugfs_create_file("interconnect_graph", 0444,
>  			    icc_debugfs_dir, NULL, &icc_graph_fops);
> +
> +	icc_debugfs_client_init(icc_debugfs_dir);
> +
>  	return 0;
>  }
>  
> diff --git a/drivers/interconnect/debugfs-client.c b/drivers/interconnect/debugfs-client.c
> new file mode 100644
> index 000000000000..990dd2ff6df7
> --- /dev/null
> +++ b/drivers/interconnect/debugfs-client.c
> @@ -0,0 +1,156 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2023, Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +#include <linux/debugfs.h>
> +#include <linux/interconnect.h>
> +#include <linux/platform_device.h>
> +#include <linux/uaccess.h>
> +

Since you are not dealing with user copy directly, I wonder why this
header inclusion is needed?

> +/*
> + * This can be dangerous, therefore don't provide any real compile time
> + * configuration option for this feature.
> + * People who want to use this will need to modify the source code directly.
> + */
> +#undef INTERCONNECT_ALLOW_WRITE_DEBUGFS
> +

Would it be nice to throw a compile error when DEBUG_FS is not enabled
but INTERCONNECT_ALLOW_WRITE_DEBUGFS is enabled?

> +#if defined(INTERCONNECT_ALLOW_WRITE_DEBUGFS) && defined(CONFIG_DEBUG_FS)
> +
> +static LIST_HEAD(debugfs_paths);
> +static DEFINE_MUTEX(debugfs_lock);
> +
> +static struct platform_device *pdev;
> +static struct icc_path *cur_path;
> +
> +static char *src_node;
> +static char *dst_node;
> +static u32 avg_bw;
> +static u32 peak_bw;
> +static u32 tag;
> +
> +struct debugfs_path {
> +	const char *src;
> +	const char *dst;
> +	struct icc_path *path;
> +	struct list_head list;
> +};
> +
> +static struct icc_path *get_path(const char *src, const char *dst)
> +{
> +	struct debugfs_path *path;
> +
> +	list_for_each_entry(path, &debugfs_paths, list) {
> +		if (!strcmp(path->src, src) && !strcmp(path->dst, dst))
> +			return path->path;
> +	}
> +
> +	return NULL;
> +}
> +
> +static int icc_get_set(void *data, u64 val)
> +{
> +	struct debugfs_path *debugfs_path;
> +	int ret = 0;
> +
> +	mutex_lock(&debugfs_lock);
> +
> +	/*
> +	 * If we've already looked up a path, then use the existing one instead
> +	 * of calling icc_get() again. This allows for updating previous BW
> +	 * votes when "get" is written to multiple times for multiple paths.
> +	 */
> +	cur_path = get_path(src_node, dst_node);
> +	if (cur_path)
> +		goto out;
> +
> +	cur_path = icc_get(&pdev->dev, src_node, dst_node);
> +	if (IS_ERR(cur_path)) {
> +		ret = PTR_ERR(cur_path);
> +		goto out;
> +	}

From the debugfs_write_file_str() implementation introduced in 1/3 of
this series, these values (src_node/dst_node) needs RCU protection.
Othewise, there is a potential UAF issue here, correct?

> +
> +	debugfs_path = kzalloc(sizeof(*debugfs_path), GFP_KERNEL);
> +	if (!debugfs_path) {
> +		ret = -ENOMEM;
> +		goto err_put;
> +	}
> +
> +	debugfs_path->path = cur_path;
> +	debugfs_path->src = kstrdup(src_node, GFP_KERNEL);
> +	debugfs_path->dst = kstrdup(dst_node, GFP_KERNEL);
> +	if (!debugfs_path->src || !debugfs_path->dst) {
> +		ret = -ENOMEM;
> +		goto err_free;
> +	}
> +
> +	list_add_tail(&debugfs_path->list, &debugfs_paths);
> +	goto out;
> +
> +err_free:
> +	kfree(debugfs_path->src);
> +	kfree(debugfs_path->dst);
> +	kfree(debugfs_path);
> +err_put:
> +	icc_put(cur_path);
> +out:
> +	mutex_unlock(&debugfs_lock);
> +	return ret;
> +}
> +
> +DEFINE_DEBUGFS_ATTRIBUTE(icc_get_fops, NULL, icc_get_set, "%llu\n");
> +
> +static int icc_commit_set(void *data, u64 val)
> +{
> +	int ret;
> +
> +	mutex_lock(&debugfs_lock);
> +
> +	if (IS_ERR_OR_NULL(cur_path)) {
> +		ret = PTR_ERR(cur_path);
> +		goto out;
> +	}
> +
> +	icc_set_tag(cur_path, tag);
> +	ret = icc_set_bw(cur_path, avg_bw, peak_bw);
> +out:
> +	mutex_unlock(&debugfs_lock);
> +	return ret;
> +}
> +
> +DEFINE_DEBUGFS_ATTRIBUTE(icc_commit_fops, NULL, icc_commit_set, "%llu\n");
> +
> +int icc_debugfs_client_init(struct dentry *icc_dir)
> +{
> +	struct dentry *client_dir;
> +	int ret;
> +
> +	pdev = platform_device_alloc("icc-debugfs-client", PLATFORM_DEVID_AUTO);
> +

In interconnect_summary debugfs file, it appears as
"icc-debugfs-client.0.auto". Since we will only ever support one
instance of this device, would PLATFORM_DEVID_NONE be more appropriate?

> +	ret = platform_device_add(pdev);
> +	if (ret) {
> +		pr_err("%s: failed to add platform device: %d\n", __func__, ret);
> +		platform_device_put(pdev);
> +		return ret;
> +	}
> +
> +	client_dir = debugfs_create_dir("test_client", icc_dir);
> +
> +	debugfs_create_str("src_node", 0600, client_dir, &src_node);
> +	debugfs_create_str("dst_node", 0600, client_dir, &dst_node);
> +	debugfs_create_file("get", 0200, client_dir, NULL, &icc_get_fops);
> +	debugfs_create_u32("avg_bw", 0600, client_dir, &avg_bw);
> +	debugfs_create_u32("peak_bw", 0600, client_dir, &peak_bw);
> +	debugfs_create_u32("tag", 0600, client_dir, &tag);
> +	debugfs_create_file("commit", 0200, client_dir, NULL, &icc_commit_fops);
> +
> +	return 0;
> +}
> +
> +#else
> +
> +int icc_debugfs_client_init(struct dentry *icc_dir)
> +{
> +	return 0;
> +}
> +
> +#endif
> diff --git a/drivers/interconnect/internal.h b/drivers/interconnect/internal.h
> index f5f82a5c939e..87152e70a99b 100644
> --- a/drivers/interconnect/internal.h
> +++ b/drivers/interconnect/internal.h
> @@ -41,4 +41,6 @@ struct icc_path {
>  	struct icc_req reqs[];
>  };
>  
> +int icc_debugfs_client_init(struct dentry *icc_dir);
> +
>  #endif
> -- 
> 2.17.1
> 

Thanks,
Pavan