Date:   Tue, 1 Dec 2020 12:26:22 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Bhaskara Budiredla <bbudiredla@...vell.com>
Cc:     ulf.hansson@...aro.org, ccross@...roid.com, tony.luck@...el.com,
        sgoutham@...vell.com, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        outgoing2/0000-cover-letter.patch@...b-0016f401.pphosted.com
Subject: Re: [PATCH v2 1/2] mmc: Support kmsg dumper based on pstore/blk

On Mon, Nov 23, 2020 at 04:49:24PM +0530, Bhaskara Budiredla wrote:
> This patch introduces to mmcpstore. The functioning of mmcpstore
> is similar to mtdpstore. mmcpstore works on FTL based flash devices
> whereas mtdpstore works on raw flash devices. When the system crashes,
> mmcpstore stores the kmsg panic and oops logs to a user specified
> MMC device.
> 
> It collects the details about the host MMC device through pstore/blk
> "blkdev" parameter. The user can specify the MMC device in many ways
> by checking in Documentation/admin-guide/pstore-blk.rst.
> 
> The individual mmc host drivers have to define suitable polling
> subroutines to write kmsg panic/oops logs through mmcpstore.
> 
> Signed-off-by: Bhaskara Budiredla <bbudiredla@...vell.com>
> ---
>  drivers/mmc/core/Kconfig     |  15 +-
>  drivers/mmc/core/Makefile    |   1 +
>  drivers/mmc/core/block.c     |  19 +++
>  drivers/mmc/core/block.h     |   9 ++
>  drivers/mmc/core/core.c      |  24 +++
>  drivers/mmc/core/mmcpstore.c | 302 +++++++++++++++++++++++++++++++++++
>  include/linux/mmc/core.h     |   4 +
>  include/linux/mmc/host.h     |  12 ++
>  8 files changed, 385 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/mmc/core/mmcpstore.c
> 
> diff --git a/drivers/mmc/core/Kconfig b/drivers/mmc/core/Kconfig
> index c12fe13e4b14..505450a6ea2b 100644
> --- a/drivers/mmc/core/Kconfig
> +++ b/drivers/mmc/core/Kconfig
> @@ -34,9 +34,23 @@ config PWRSEQ_SIMPLE
>  	  This driver can also be built as a module. If so, the module
>  	  will be called pwrseq_simple.
>  
> +config MMC_PSTORE_BACKEND
> +	bool "Log panic/oops to a MMC buffer"
> +	depends on MMC_BLOCK
> +	default n

"default n" is redundant and can be dropped.

> +	help
> +	  This option will let you create platform backend to store kmsg
> +	  crash dumps to a user specified MMC device. This is primarily
> +	  based on pstore/blk.
> +
> +config MMC_PSTORE
> +	tristate
> +	select PSTORE_BLK

I don't understand why this is separate?

> +
>  config MMC_BLOCK
>  	tristate "MMC block device driver"
>  	depends on BLOCK
> +	select MMC_PSTORE if MMC_PSTORE_BACKEND=y
>  	default y
>  	help
>  	  Say Y here to enable the MMC block device driver support.
> @@ -80,4 +94,3 @@ config MMC_TEST
>  
>  	  This driver is only of interest to those developing or
>  	  testing a host driver. Most people should say N here.
> -

Why isn't this just written as:

config MMC_PSTORE
	bool "Log panic/oops to a MMC buffer"
	depends on MMC_BLOCK
	select PSTORE_BLK
	help
	  This option will let you create platform backend to store kmsg
	  crash dumps to a user specified MMC device. This is primarily
	  based on pstore/blk.




> diff --git a/drivers/mmc/core/Makefile b/drivers/mmc/core/Makefile
> index 95ffe008ebdf..7cb9a3af4827 100644
> --- a/drivers/mmc/core/Makefile
> +++ b/drivers/mmc/core/Makefile
> @@ -16,5 +16,6 @@ obj-$(CONFIG_PWRSEQ_EMMC)	+= pwrseq_emmc.o
>  mmc_core-$(CONFIG_DEBUG_FS)	+= debugfs.o
>  obj-$(CONFIG_MMC_BLOCK)		+= mmc_block.o
>  mmc_block-objs			:= block.o queue.o
> +mmc_block-$(CONFIG_MMC_PSTORE)	+= mmcpstore.o
>  obj-$(CONFIG_MMC_TEST)		+= mmc_test.o
>  obj-$(CONFIG_SDIO_UART)		+= sdio_uart.o
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index 8d3df0be0355..ed012a91e3a3 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -2870,6 +2870,21 @@ static void mmc_blk_remove_debugfs(struct mmc_card *card,
>  
>  #endif /* CONFIG_DEBUG_FS */
>  
> +#if IS_ENABLED(CONFIG_MMC_PSTORE)
> +sector_t mmc_blk_get_part(struct mmc_card *card, int part_num, sector_t *size)
> +{
> +	struct mmc_blk_data *md = dev_get_drvdata(&card->dev);
> +	struct gendisk *disk = md->disk;
> +	struct disk_part_tbl *part_tbl = disk->part_tbl;
> +
> +	if (part_num < 0 || part_num >= part_tbl->len)
> +		return 0;
> +
> +	*size = part_tbl->part[part_num]->nr_sects << SECTOR_SHIFT;
> +	return part_tbl->part[part_num]->start_sect;
> +}
> +#endif
> +
>  static int mmc_blk_probe(struct mmc_card *card)
>  {
>  	struct mmc_blk_data *md, *part_md;
> @@ -2913,6 +2928,9 @@ static int mmc_blk_probe(struct mmc_card *card)
>  			goto out;
>  	}
>  
> +	if (mmc_card_mmc(card) || mmc_card_sd(card))
> +		mmcpstore_card_set(card, md->disk->disk_name);
> +
>  	/* Add two debugfs entries */
>  	mmc_blk_add_debugfs(card, md);
>  
> @@ -3060,6 +3078,7 @@ static void __exit mmc_blk_exit(void)
>  	unregister_blkdev(MMC_BLOCK_MAJOR, "mmc");
>  	unregister_chrdev_region(mmc_rpmb_devt, MAX_DEVICES);
>  	bus_unregister(&mmc_rpmb_bus_type);
> +	unregister_mmcpstore();
>  }
>  
>  module_init(mmc_blk_init);
> diff --git a/drivers/mmc/core/block.h b/drivers/mmc/core/block.h
> index 31153f656f41..2a4ee5568194 100644
> --- a/drivers/mmc/core/block.h
> +++ b/drivers/mmc/core/block.h
> @@ -16,5 +16,14 @@ void mmc_blk_mq_recovery(struct mmc_queue *mq);
>  struct work_struct;
>  
>  void mmc_blk_mq_complete_work(struct work_struct *work);
> +#if IS_ENABLED(CONFIG_MMC_PSTORE)
> +sector_t mmc_blk_get_part(struct mmc_card *card, int part_num, sector_t *size);
> +void mmcpstore_card_set(struct mmc_card *card, const char *disk_name);
> +void unregister_mmcpstore(void);
> +#else
> +static inline void mmcpstore_card_set(struct mmc_card *card,
> +					const char *disk_name) {}
> +static inline void unregister_mmcpstore(void) {}
> +#endif
>  
>  #endif
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index d42037f0f10d..7682b267f1d5 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -569,6 +569,30 @@ int mmc_cqe_recovery(struct mmc_host *host)
>  }
>  EXPORT_SYMBOL(mmc_cqe_recovery);
>  
> +#if IS_ENABLED(CONFIG_MMC_PSTORE)
> +/**
> + *	mmc_wait_for_pstore_req - initiate a blocking mmc request
> + *	@host: MMC host to start command
> + *	@mrq: MMC request to start
> + *
> + *	Start a blocking MMC request for a host and wait for the request
> + *	to complete that is based on polling and timeout.
> + */
> +void mmc_wait_for_pstore_req(struct mmc_host *host, struct mmc_request *mrq)
> +{
> +	unsigned int timeout;
> +
> +	host->ops->req_cleanup_pending(host);
> +	mmc_start_request(host, mrq);
> +
> +	if (mrq->data) {
> +		timeout = mrq->data->timeout_ns / NSEC_PER_MSEC;
> +		host->ops->req_completion_poll(host, timeout);
> +	}
> +}
> +EXPORT_SYMBOL(mmc_wait_for_pstore_req);
> +#endif
> +
>  /**
>   *	mmc_is_req_done - Determine if a 'cap_cmd_during_tfr' request is done
>   *	@host: MMC host
> diff --git a/drivers/mmc/core/mmcpstore.c b/drivers/mmc/core/mmcpstore.c
> new file mode 100644
> index 000000000000..1113eae0756c
> --- /dev/null
> +++ b/drivers/mmc/core/mmcpstore.c
> @@ -0,0 +1,302 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * MMC pstore support based on pstore/blk
> + *
> + * Copyright (c) 2020 Marvell.
> + * Author: Bhaskara Budiredla <bbudiredla@...vell.com>
> + */
> +
> +#define pr_fmt(fmt) "mmcpstore: " fmt
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/pstore_blk.h>
> +#include <linux/blkdev.h>
> +#include <linux/mount.h>
> +#include <linux/slab.h>
> +#include <linux/mmc/mmc.h>
> +#include <linux/mmc/host.h>
> +#include <linux/mmc/card.h>
> +#include <linux/scatterlist.h>
> +#include "block.h"
> +#include "card.h"
> +#include "core.h"
> +
> +static struct mmcpstore_context {
> +	char dev_name[BDEVNAME_SIZE];
> +	int partno;
> +	sector_t start_sect;
> +	sector_t size;
> +	struct pstore_device_info dev;
> +	struct pstore_blk_config conf;
> +	struct pstore_blk_info info;
> +
> +	char *sub;
> +	struct mmc_card	*card;
> +	struct mmc_request *mrq;
> +} oops_cxt;
> +
> +static void mmc_prep_req(struct mmc_request *mrq,
> +		unsigned int sect_offset, unsigned int nsects,
> +		struct scatterlist *sg, u32 opcode, unsigned int flags)
> +{
> +	mrq->cmd->opcode = opcode;
> +	mrq->cmd->arg = sect_offset;
> +	mrq->cmd->flags = MMC_RSP_R1 | MMC_CMD_ADTC;
> +
> +	if (nsects == 1) {
> +		mrq->stop = NULL;
> +	} else {
> +		mrq->stop->opcode = MMC_STOP_TRANSMISSION;
> +		mrq->stop->arg = 0;
> +		mrq->stop->flags = MMC_RSP_R1B | MMC_CMD_AC;
> +	}
> +
> +	mrq->data->blksz = SECTOR_SIZE;
> +	mrq->data->blocks = nsects;
> +	mrq->data->flags = flags;
> +	mrq->data->sg = sg;
> +	mrq->data->sg_len = 1;
> +}
> +
> +static int mmcpstore_rdwr_req(const char *buf, unsigned int nsects,
> +			unsigned int sect_offset, unsigned int flags)
> +{
> +	struct mmcpstore_context *cxt = &oops_cxt;
> +	struct mmc_request *mrq = cxt->mrq;
> +	struct mmc_card *card = cxt->card;
> +	struct mmc_host *host = card->host;
> +	struct scatterlist sg;
> +	u32 opcode;
> +
> +	if (flags == MMC_DATA_READ)
> +		opcode	= (nsects > 1) ?
> +			MMC_READ_MULTIPLE_BLOCK : MMC_READ_SINGLE_BLOCK;
> +	else
> +		opcode = (nsects > 1) ?
> +			MMC_WRITE_MULTIPLE_BLOCK : MMC_WRITE_BLOCK;
> +
> +	mmc_prep_req(mrq, sect_offset, nsects, &sg, opcode, flags);
> +	sg_init_one(&sg, buf, (nsects << SECTOR_SHIFT));
> +	mmc_set_data_timeout(mrq->data, cxt->card);
> +
> +	mmc_claim_host(host);
> +	mmc_wait_for_req(host, mrq);
> +	mdelay(mrq->data->timeout_ns / NSEC_PER_MSEC);
> +	mmc_release_host(host);
> +
> +	if (mrq->cmd->error) {
> +		pr_err("Cmd error: %d\n", mrq->cmd->error);
> +		return mrq->cmd->error;
> +	}
> +	if (mrq->data->error) {
> +		pr_err("Data error: %d\n", mrq->data->error);
> +		return mrq->data->error;
> +	}
> +
> +	return 0;
> +}
> +
> +static ssize_t mmcpstore_write(const char *buf, size_t size, loff_t off)
> +{
> +	struct mmcpstore_context *cxt = &oops_cxt;
> +	int ret;
> +
> +	ret = mmcpstore_rdwr_req(buf, (size >> SECTOR_SHIFT),
> +		cxt->start_sect + (off >> SECTOR_SHIFT), MMC_DATA_WRITE);
> +	if (ret)
> +		return ret;
> +
> +	return size;
> +}
> +
> +static ssize_t mmcpstore_read(char *buf, size_t size, loff_t off)
> +{
> +	struct mmcpstore_context *cxt = &oops_cxt;
> +	unsigned int sect_off = cxt->start_sect  + (off >> SECTOR_SHIFT);
> +	unsigned long sects = (cxt->conf.kmsg_size >> SECTOR_SHIFT);
> +	int ret;
> +
> +	if (unlikely(!buf || !size))
> +		return -EINVAL;
> +
> +	ret = mmcpstore_rdwr_req(cxt->sub, sects, sect_off, MMC_DATA_READ);
> +	if (ret)
> +		return ret;
> +	memcpy(buf, cxt->sub, size);
> +
> +	return size;
> +}
> +
> +static void mmcpstore_panic_write_req(const char *buf,
> +		unsigned int nsects, unsigned int sect_offset)
> +{
> +	struct mmcpstore_context *cxt = &oops_cxt;
> +	struct mmc_request *mrq = cxt->mrq;
> +	struct mmc_card *card = cxt->card;
> +	struct mmc_host *host = card->host;
> +	struct scatterlist sg;
> +	u32 opcode;
> +
> +	opcode = (nsects > 1) ? MMC_WRITE_MULTIPLE_BLOCK : MMC_WRITE_BLOCK;
> +	mmc_prep_req(mrq, sect_offset, nsects, &sg, opcode, MMC_DATA_WRITE);
> +	sg_init_one(&sg, buf, (nsects << SECTOR_SHIFT));
> +	mmc_set_data_timeout(mrq->data, cxt->card);
> +
> +	mmc_claim_host(host);
> +	mmc_wait_for_pstore_req(host, mrq);
> +	mmc_release_host(card->host);
> +}
> +
> +static ssize_t mmcpstore_panic_write(const char *buf, size_t size, loff_t off)
> +{
> +	struct mmcpstore_context *cxt = &oops_cxt;
> +
> +	mmcpstore_panic_write_req(buf, (size >> SECTOR_SHIFT),
> +			cxt->start_sect + (off >> SECTOR_SHIFT));
> +	return size;
> +}
> +
> +static struct block_device *mmcpstore_open_backend(const char *device)
> +{
> +	struct block_device *bdev;
> +	dev_t devt;
> +
> +	bdev = blkdev_get_by_path(device, FMODE_READ, NULL);
> +	if (IS_ERR(bdev)) {
> +		devt = name_to_dev_t(device);
> +		if (devt == 0)
> +			return ERR_PTR(-ENODEV);
> +
> +		bdev = blkdev_get_by_dev(devt, FMODE_READ, NULL);
> +		if (IS_ERR(bdev))
> +			return bdev;
> +	}
> +
> +	return bdev;
> +}
> +
> +static void mmcpstore_close_backend(struct block_device *bdev)
> +{
> +	if (!bdev)
> +		return;
> +	blkdev_put(bdev, FMODE_READ);
> +}
> +
> +void mmcpstore_card_set(struct mmc_card *card, const char *disk_name)
> +{
> +	struct mmcpstore_context *cxt = &oops_cxt;
> +	struct pstore_blk_config *conf = &cxt->conf;
> +	struct pstore_device_info *dev = &cxt->dev;
> +	struct block_device *bdev;
> +	struct mmc_command *stop;
> +	struct mmc_command *cmd;
> +	struct mmc_request *mrq;
> +	struct mmc_data *data;
> +	int ret;
> +
> +	ret = pstore_blk_get_config(conf);
> +	if (!conf->device[0]) {
> +		pr_debug("psblk backend is empty\n");
> +		return;
> +	}
> +
> +	/* Multiple backend devices not allowed */
> +	if (cxt->dev_name[0])
> +		return;
> +
> +	bdev =  mmcpstore_open_backend(conf->device);
> +	if (IS_ERR(bdev)) {
> +		pr_err("%s failed to open with %ld\n",
> +				conf->device, PTR_ERR(bdev));
> +		return;
> +	}
> +
> +	bdevname(bdev, cxt->dev_name);
> +	cxt->partno = bdev->bd_part->partno;
> +	mmcpstore_close_backend(bdev);
> +
> +	if (strncmp(cxt->dev_name, disk_name, strlen(disk_name)))
> +		return;

Why isn't this just strcmp()?

> +
> +	cxt->start_sect = mmc_blk_get_part(card, cxt->partno, &cxt->size);
> +	if (!cxt->start_sect) {
> +		pr_err("Non-existent partition %d selected\n", cxt->partno);
> +		return;
> +	}
> +
> +	/* Check for host mmc panic write polling function definitions */
> +	if (!card->host->ops->req_cleanup_pending ||
> +			!card->host->ops->req_completion_poll)
> +		return;
> +
> +	cxt->card = card;
> +
> +	cxt->sub = kmalloc(conf->kmsg_size, GFP_KERNEL);
> +	if (!cxt->sub)
> +		goto out;
> +
> +	mrq = kzalloc(sizeof(struct mmc_request), GFP_KERNEL);
> +	if (!mrq)
> +		goto free_sub;
> +
> +	cmd = kzalloc(sizeof(struct mmc_command), GFP_KERNEL);
> +	if (!cmd)
> +		goto free_mrq;
> +
> +	stop = kzalloc(sizeof(struct mmc_command), GFP_KERNEL);
> +	if (!stop)
> +		goto free_cmd;
> +
> +	data = kzalloc(sizeof(struct mmc_data), GFP_KERNEL);
> +	if (!data)
> +		goto free_stop;
> +
> +	mrq->cmd = cmd;
> +	mrq->data = data;
> +	mrq->stop = stop;
> +	cxt->mrq = mrq;
> +
> +	dev->total_size = cxt->size;
> +	dev->flags = PSTORE_FLAGS_DMESG;

Can't this support more than just DMESG? I don't see anything specific
to that. This is using pstore/zone ultimately, which can support
whatever frontends it needs to.

> +	dev->read = mmcpstore_read;
> +	dev->write = mmcpstore_write;
> +	dev->erase = NULL;

No way to remove the records?

> +	dev->panic_write = mmcpstore_panic_write;
> +
> +	ret = register_pstore_device(&cxt->dev);
> +	if (ret) {
> +		pr_err("%s registering with psblk failed (%d)\n",
> +				cxt->dev_name, ret);
> +		goto free_data;
> +	}
> +
> +	pr_info("%s registered as psblk backend\n", cxt->dev_name);
> +	return;
> +
> +free_data:
> +	kfree(data);
> +free_stop:
> +	kfree(stop);
> +free_cmd:
> +	kfree(cmd);
> +free_mrq:
> +	kfree(mrq);
> +free_sub:
> +	kfree(cxt->sub);
> +out:
> +	return;
> +}
> +
> +void unregister_mmcpstore(void)
> +{
> +	struct mmcpstore_context *cxt = &oops_cxt;
> +
> +	unregister_pstore_device(&cxt->dev);
> +	kfree(cxt->mrq->data);
> +	kfree(cxt->mrq->stop);
> +	kfree(cxt->mrq->cmd);
> +	kfree(cxt->mrq);
> +	kfree(cxt->sub);
> +	cxt->card = NULL;
> +}
> diff --git a/include/linux/mmc/core.h b/include/linux/mmc/core.h
> index 29aa50711626..3889c2a90faa 100644
> --- a/include/linux/mmc/core.h
> +++ b/include/linux/mmc/core.h
> @@ -166,6 +166,10 @@ struct mmc_request {
>  
>  struct mmc_card;
>  
> +#if IS_ENABLED(CONFIG_MMC_PSTORE)
> +void mmc_wait_for_pstore_req(struct mmc_host *, struct mmc_request *);
> +#endif
> +
>  void mmc_wait_for_req(struct mmc_host *host, struct mmc_request *mrq);
>  int mmc_wait_for_cmd(struct mmc_host *host, struct mmc_command *cmd,
>  		int retries);
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index c079b932330f..7d6751005ac6 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -173,6 +173,18 @@ struct mmc_host_ops {
>  	 */
>  	int	(*multi_io_quirk)(struct mmc_card *card,
>  				  unsigned int direction, int blk_size);
> +
> +#if IS_ENABLED(CONFIG_MMC_PSTORE)
> +	/*
> +	 * The following two APIs are introduced to support mmcpstore
> +	 * functionality. Cleanup API to terminate the ongoing and
> +	 * pending requests before a panic write post, and polling API
> +	 * to ensure that write succeeds before the Kernel dies.
> +	 */
> +	void	(*req_cleanup_pending)(struct mmc_host *host);
> +	int	(*req_completion_poll)(struct mmc_host *host,
> +					unsigned long timeout);
> +#endif
>  };
>  
>  struct mmc_cqe_ops {
> -- 
> 2.17.1
> 

Otherwise, sure, this looks good to me as far as pstore is concerned.

-- 
Kees Cook

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