Re: [PATCH 2/2] pmem: add a driver for persistent memory

[Boaz Harrosh]

On 04/01/2015 10:12 AM, Christoph Hellwig wrote:
> From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> 
> PMEM is a new driver that presents a reserved range of memory as a
> block device.  This is useful for developing with NV-DIMMs, and
> can be used with volatile memory as a development platform.
> 
> This patch contains the initial driver from Ross Zwisler, with
> various changes from Boaz Harrosh and me.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> [hch: convert to use a platform_device for discovery, fix partition
>  support, merged various patches from Boaz]
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> Tested-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
>  MAINTAINERS            |   6 ++
>  drivers/block/Kconfig  |  11 +++
>  drivers/block/Makefile |   1 +
>  drivers/block/pmem.c   | 260 +++++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 278 insertions(+)
>  create mode 100644 drivers/block/pmem.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 1de6afa..4517613 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8071,6 +8071,12 @@ S:	Maintained
>  F:	Documentation/blockdev/ramdisk.txt
>  F:	drivers/block/brd.c
>  
> +PERSISTENT MEMORY DRIVER
> +M:	Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> +L:	linux-nvdimm@xxxxxxxxxxxx
> +S:	Supported
> +F:	drivers/block/pmem.c
> +
>  RANDOM NUMBER DRIVER
>  M:	"Theodore Ts'o" <tytso@xxxxxxx>
>  S:	Maintained
> diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
> index 1b8094d..34753cf 100644
> --- a/drivers/block/Kconfig
> +++ b/drivers/block/Kconfig
> @@ -404,6 +404,17 @@ config BLK_DEV_RAM_DAX
>  	  and will prevent RAM block device backing store memory from being
>  	  allocated from highmem (only a problem for highmem systems).
>  
> +config BLK_DEV_PMEM
> +	tristate "Persistent memory block device support"
> +	help
> +	  Saying Y here will allow you to use a contiguous range of reserved
> +	  memory as one or more block devices.
> +
> +	  To compile this driver as a module, choose M here: the module will be
> +	  called pmem.
> +
> +	  If unsure, say N.
> +
>  config CDROM_PKTCDVD
>  	tristate "Packet writing on CD/DVD media"
>  	depends on !UML
> diff --git a/drivers/block/Makefile b/drivers/block/Makefile
> index 02b688d..9cc6c18 100644
> --- a/drivers/block/Makefile
> +++ b/drivers/block/Makefile
> @@ -14,6 +14,7 @@ obj-$(CONFIG_PS3_VRAM)		+= ps3vram.o
>  obj-$(CONFIG_ATARI_FLOPPY)	+= ataflop.o
>  obj-$(CONFIG_AMIGA_Z2RAM)	+= z2ram.o
>  obj-$(CONFIG_BLK_DEV_RAM)	+= brd.o
> +obj-$(CONFIG_BLK_DEV_PMEM)	+= pmem.o
>  obj-$(CONFIG_BLK_DEV_LOOP)	+= loop.o
>  obj-$(CONFIG_BLK_CPQ_DA)	+= cpqarray.o
>  obj-$(CONFIG_BLK_CPQ_CISS_DA)  += cciss.o
> diff --git a/drivers/block/pmem.c b/drivers/block/pmem.c
> new file mode 100644
> index 0000000..0232ab7
> --- /dev/null
> +++ b/drivers/block/pmem.c
> @@ -0,0 +1,260 @@
> +/*
> + * Persistent Memory Driver
> + * Copyright (c) 2014, Intel Corporation.
> + * Copyright (c) 2015, Christoph Hellwig <hch@xxxxxx>.
> + * Copyright (c) 2015, Boaz Harrosh <boaz@xxxxxxxxxxxxx>.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + */
> +
> +#include <asm/cacheflush.h>
> +#include <linux/blkdev.h>
> +#include <linux/hdreg.h>
> +#include <linux/init.h>
> +#include <linux/platform_device.h>
> +#include <linux/module.h>
> +#include <linux/moduleparam.h>
> +#include <linux/slab.h>
> +
> +#define PMEM_MINORS		16
> +
> +struct pmem_device {
> +	struct request_queue	*pmem_queue;
> +	struct gendisk		*pmem_disk;
> +
> +	/* One contiguous memory region per device */
> +	phys_addr_t		phys_addr;
> +	void			*virt_addr;
> +	size_t			size;
> +};
> +
> +static int pmem_major;
> +static atomic_t pmem_index;
> +
> +static void pmem_do_bvec(struct pmem_device *pmem, struct page *page,
> +			unsigned int len, unsigned int off, int rw,
> +			sector_t sector)
> +{
> +	void *mem = kmap_atomic(page);
> +	size_t pmem_off = sector << 9;
> +
> +	if (rw == READ) {
> +		memcpy(mem + off, pmem->virt_addr + pmem_off, len);
> +		flush_dcache_page(page);
> +	} else {
> +		flush_dcache_page(page);
> +		memcpy(pmem->virt_addr + pmem_off, mem + off, len);
> +	}
> +
> +	kunmap_atomic(mem);
> +}
> +
> +static void pmem_make_request(struct request_queue *q, struct bio *bio)
> +{
> +	struct block_device *bdev = bio->bi_bdev;
> +	struct pmem_device *pmem = bdev->bd_disk->private_data;
> +	int rw;
> +	struct bio_vec bvec;
> +	sector_t sector;
> +	struct bvec_iter iter;
> +	int err = 0;
> +
> +	if (bio_end_sector(bio) > get_capacity(bdev->bd_disk)) {
> +		err = -EIO;
> +		goto out;
> +	}
> +
> +	BUG_ON(bio->bi_rw & REQ_DISCARD);
> +
> +	rw = bio_data_dir(bio);

OK cool I was afraid since you did not like my unlikely patch
that you might have missed this fix.

> +	sector = bio->bi_iter.bi_sector;
> +	bio_for_each_segment(bvec, bio, iter) {
> +		pmem_do_bvec(pmem, bvec.bv_page, bvec.bv_len, bvec.bv_offset,
> +			     rw, sector);
> +		sector += bvec.bv_len >> 9;
> +	}
> +
> +out:
> +	bio_endio(bio, err);
> +}
> +
> +static int pmem_rw_page(struct block_device *bdev, sector_t sector,
> +		       struct page *page, int rw)
> +{
> +	struct pmem_device *pmem = bdev->bd_disk->private_data;
> +
> +	pmem_do_bvec(pmem, page, PAGE_CACHE_SIZE, 0, rw, sector);
> +	page_endio(page, rw & WRITE, 0);

You might as well rw & WRITE also for the above pmem_do_bvec call.
If there can be such problem than the rw == READ inside
pmem_do_bvec will fail as well.

> +	return 0;
> +}
> +
> +static long pmem_direct_access(struct block_device *bdev, sector_t sector,
> +			      void **kaddr, unsigned long *pfn, long size)
> +{
> +	struct pmem_device *pmem = bdev->bd_disk->private_data;
> +	size_t offset = sector << 9;
> +
> +	if (!pmem)
> +		return -ENODEV;
> +
> +	*kaddr = pmem->virt_addr + offset;
> +	*pfn = (pmem->phys_addr + offset) >> PAGE_SHIFT;
> +
> +	return pmem->size - offset;
> +}
> +
> +static const struct block_device_operations pmem_fops = {
> +	.owner =		THIS_MODULE,
> +	.rw_page =		pmem_rw_page,
> +	.direct_access =	pmem_direct_access,
> +};
> +
> +static struct pmem_device *pmem_alloc(struct device *dev, struct resource *res)
> +{
> +	struct pmem_device *pmem;
> +	struct gendisk *disk;
> +	int idx, err;
> +
> +	err = -ENOMEM;
> +	pmem = kzalloc(sizeof(*pmem), GFP_KERNEL);
> +	if (!pmem)
> +		goto out;
> +
> +	pmem->phys_addr = res->start;
> +	pmem->size = resource_size(res);
> +
> +	err = -EINVAL;
> +	if (!request_mem_region(pmem->phys_addr, pmem->size, "pmem")) {
> +		dev_warn(dev, "could not reserve region [0x%llx:0x%zx]\n",
> +			   pmem->phys_addr, pmem->size);
> +		goto out_free_dev;
> +	}
> +
> +	/*
> +	 * Map the memory as non-cachable, as we can't write back the contents
> +	 * of the CPU caches in case of a crash.
> +	 */
> +	err = -ENOMEM;
> +	pmem->virt_addr = ioremap_nocache(pmem->phys_addr, pmem->size);
> +	if (!pmem->virt_addr)
> +		goto out_release_region;

You have removed the pmem_mapmem() helper and embedded all this here.
The patch to add page-structs that I'm posting on top of
this, uses the abstraction to switch between implementations.

I'll add the split-out to the page-structs patch.

Am heavy testing this set (Together with my small fix to e820)
And will report tomorrow if the lab is able to survive the night.

Thanks
Boaz

> +
> +	pmem->pmem_queue = blk_alloc_queue(GFP_KERNEL);
> +	if (!pmem->pmem_queue)
> +		goto out_unmap;
> +
> +	blk_queue_make_request(pmem->pmem_queue, pmem_make_request);
> +	blk_queue_max_hw_sectors(pmem->pmem_queue, 1024);
> +	blk_queue_bounce_limit(pmem->pmem_queue, BLK_BOUNCE_ANY);
> +
> +	disk = alloc_disk(PMEM_MINORS);
> +	if (!disk)
> +		goto out_free_queue;
> +
> +	idx = atomic_inc_return(&pmem_index) - 1;
> +
> +	disk->major		= pmem_major;
> +	disk->first_minor	= PMEM_MINORS * idx;
> +	disk->fops		= &pmem_fops;
> +	disk->private_data	= pmem;
> +	disk->queue		= pmem->pmem_queue;
> +	disk->flags		= GENHD_FL_EXT_DEVT;
> +	sprintf(disk->disk_name, "pmem%d", idx);
> +	disk->driverfs_dev = dev;
> +	set_capacity(disk, pmem->size >> 9);
> +	pmem->pmem_disk = disk;
> +
> +	add_disk(disk);
> +	return pmem;
> +
> +out_free_queue:
> +	blk_cleanup_queue(pmem->pmem_queue);
> +out_unmap:
> +	iounmap(pmem->virt_addr);
> +out_release_region:
> +	release_mem_region(pmem->phys_addr, pmem->size);
> +out_free_dev:
> +	kfree(pmem);
> +out:
> +	return ERR_PTR(err);
> +}
> +
> +static void pmem_free(struct pmem_device *pmem)
> +{
> +	del_gendisk(pmem->pmem_disk);
> +	put_disk(pmem->pmem_disk);
> +	blk_cleanup_queue(pmem->pmem_queue);
> +	iounmap(pmem->virt_addr);
> +	release_mem_region(pmem->phys_addr, pmem->size);
> +	kfree(pmem);
> +}
> +
> +static int pmem_probe(struct platform_device *pdev)
> +{
> +	struct pmem_device *pmem;
> +	struct resource *res;
> +
> +	if (WARN_ON(pdev->num_resources > 1))
> +		return -ENXIO;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	if (!res)
> +		return -ENXIO;
> +
> +	pmem = pmem_alloc(&pdev->dev, res);
> +	if (IS_ERR(pmem))
> +		return PTR_ERR(pmem);
> +
> +	platform_set_drvdata(pdev, pmem);
> +	return 0;
> +}
> +
> +static int pmem_remove(struct platform_device *pdev)
> +{
> +	struct pmem_device *pmem = platform_get_drvdata(pdev);
> +
> +	pmem_free(pmem);
> +	return 0;
> +}
> +
> +static struct platform_driver pmem_driver = {
> +	.probe		= pmem_probe,
> +	.remove		= pmem_remove,
> +	.driver		= {
> +		.owner	= THIS_MODULE,
> +		.name	= "pmem",
> +	},
> +};
> +
> +static int __init pmem_init(void)
> +{
> +	int error;
> +
> +	pmem_major = register_blkdev(0, "pmem");
> +	if (pmem_major < 0)
> +		return pmem_major;
> +
> +	error = platform_driver_register(&pmem_driver);
> +	if (error)
> +		unregister_blkdev(pmem_major, "pmem");
> +	return error;
> +}
> +
> +static void pmem_exit(void)
> +{
> +	platform_driver_unregister(&pmem_driver);
> +	unregister_blkdev(pmem_major, "pmem");
> +}
> +
> +MODULE_AUTHOR("Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>");
> +MODULE_LICENSE("GPL v2");
> +
> +module_init(pmem_init);
> +module_exit(pmem_exit);
> 

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