[PATCH v5 4/5] dax: fix mapping lifetime handling, convert to __pfn_t + kmap_atomic_pfn_t()

From: Dan Williams
Date: Wed Aug 12 2015 - 23:07:47 EST

The primary source for non-page-backed page-frames to enter the system
is via the pmem driver's ->direct_access() method. The pfns returned by
the top-level bdev_direct_access() may be passed to any other subsystem
in the kernel and those sub-systems either need to assume that the pfn
is page backed (CONFIG_DEV_PFN=n) or be prepared to handle non-page
backed case (CONFIG_DEV_PFN=y). Currently the pfns returned by
->direct_access() are only ever used by vm_insert_mixed() which does not
care if the pfn is mapped. As we go to add more usages of these pfns
add the type-safety of __pfn_t.

This also simplifies the calling convention of ->direct_access() by not
returning the virtual address in the same call. This annotates cases
where the kernel is directly accessing pmem outside the driver, and
makes the valid lifetime of the reference explicit. This property may
be useful in the future for invalidating mappings to pmem, but for now
it provides some protection against the "pmem disable vs still-in-use"
race.

Note that axon_ram_direct_access and dcssblk_direct_access were
previously making potentially incorrect assumptions about the addresses
they passed to virt_to_phys().

[hch: various minor updates]
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
arch/powerpc/platforms/Kconfig | 1 +
arch/powerpc/sysdev/axonram.c | 24 ++++++++----
drivers/block/brd.c | 5 +--
drivers/nvdimm/Kconfig | 1 +
drivers/nvdimm/pmem.c | 24 +++++++-----
drivers/s390/block/Kconfig | 1 +
drivers/s390/block/dcssblk.c | 23 ++++++++++--
fs/Kconfig | 1 +
fs/block_dev.c | 4 +-
fs/dax.c | 79 +++++++++++++++++++++++++++++-----------
include/linux/blkdev.h | 7 ++--
include/linux/mm.h | 12 ++++++
12 files changed, 129 insertions(+), 53 deletions(-)

diff --git a/arch/powerpc/platforms/Kconfig b/arch/powerpc/platforms/Kconfig
index b7f9c408bf24..6b1c2f2e5fb4 100644
--- a/arch/powerpc/platforms/Kconfig
+++ b/arch/powerpc/platforms/Kconfig
@@ -307,6 +307,7 @@ config CPM2
config AXON_RAM
tristate "Axon DDR2 memory device driver"
depends on PPC_IBM_CELL_BLADE && BLOCK
+ select KMAP_PFN
default m
help
It registers one block device per Axon's DDR2 memory bank found
diff --git a/arch/powerpc/sysdev/axonram.c b/arch/powerpc/sysdev/axonram.c
index e8657d3bc588..7c5a1563c0fd 100644
--- a/arch/powerpc/sysdev/axonram.c
+++ b/arch/powerpc/sysdev/axonram.c
@@ -43,6 +43,7 @@
#include <linux/types.h>
#include <linux/of_device.h>
#include <linux/of_platform.h>
+#include <linux/kmap_pfn.h>

#include <asm/page.h>
#include <asm/prom.h>
@@ -141,14 +142,12 @@ axon_ram_make_request(struct request_queue *queue, struct bio *bio)
*/
static long
axon_ram_direct_access(struct block_device *device, sector_t sector,
- void **kaddr, unsigned long *pfn)
+ __pfn_t *pfn)
{
struct axon_ram_bank *bank = device->bd_disk->private_data;
loff_t offset = (loff_t)sector << AXON_RAM_SECTOR_SHIFT;

- *kaddr = (void *)(bank->ph_addr + offset);
- *pfn = virt_to_phys(*kaddr) >> PAGE_SHIFT;
-
+ *pfn = phys_to_pfn_t(bank->ph_addr + offset, PFN_DEV);
return bank->size - offset;
}

@@ -165,9 +164,13 @@ static int axon_ram_probe(struct platform_device *device)
{
static int axon_ram_bank_id = -1;
struct axon_ram_bank *bank;
- struct resource resource;
+ struct resource *resource;
int rc = 0;

+ resource = devm_kzalloc(&device->dev, sizeof(*resource), GFP_KERNEL);
+ if (!resource)
+ return -ENOMEM;
+
axon_ram_bank_id++;

dev_info(&device->dev, "Found memory controller on %s\n",
@@ -184,13 +187,13 @@ static int axon_ram_probe(struct platform_device *device)

bank->device = device;

- if (of_address_to_resource(device->dev.of_node, 0, &resource) != 0) {
+ if (of_address_to_resource(device->dev.of_node, 0, resource) != 0) {
dev_err(&device->dev, "Cannot access device tree\n");
rc = -EFAULT;
goto failed;
}

- bank->size = resource_size(&resource);
+ bank->size = resource_size(resource);

if (bank->size == 0) {
dev_err(&device->dev, "No DDR2 memory found for %s%d\n",
@@ -202,7 +205,7 @@ static int axon_ram_probe(struct platform_device *device)
dev_info(&device->dev, "Register DDR2 memory device %s%d with %luMB\n",
AXON_RAM_DEVICE_NAME, axon_ram_bank_id, bank->size >> 20);

- bank->ph_addr = resource.start;
+ bank->ph_addr = resource->start;
bank->io_addr = (unsigned long) ioremap_prot(
bank->ph_addr, bank->size, _PAGE_NO_CACHE);
if (bank->io_addr == 0) {
@@ -211,6 +214,11 @@ static int axon_ram_probe(struct platform_device *device)
goto failed;
}

+ rc = devm_register_kmap_pfn_range(&device->dev, resource,
+ (void *) bank->io_addr);
+ if (rc)
+ goto failed;
+
bank->disk = alloc_disk(AXON_RAM_MINORS_PER_DISK);
if (bank->disk == NULL) {
dev_err(&device->dev, "Cannot register disk\n");
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 41528857c70d..6c4b21a4e915 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -371,7 +371,7 @@ static int brd_rw_page(struct block_device *bdev, sector_t sector,

#ifdef CONFIG_BLK_DEV_RAM_DAX
static long brd_direct_access(struct block_device *bdev, sector_t sector,
- void **kaddr, unsigned long *pfn)
+ __pfn_t *pfn)
{
struct brd_device *brd = bdev->bd_disk->private_data;
struct page *page;
@@ -381,8 +381,7 @@ static long brd_direct_access(struct block_device *bdev, sector_t sector,
page = brd_insert_page(brd, sector);
if (!page)
return -ENOSPC;
- *kaddr = page_address(page);
- *pfn = page_to_pfn(page);
+ *pfn = page_to_pfn_t(page);

return PAGE_SIZE;
}
diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig
index 72226acb5c0f..0d8c6bda7a41 100644
--- a/drivers/nvdimm/Kconfig
+++ b/drivers/nvdimm/Kconfig
@@ -20,6 +20,7 @@ config BLK_DEV_PMEM
tristate "PMEM: Persistent memory block device support"
default LIBNVDIMM
depends on HAS_IOMEM
+ select KMAP_PFN
select ND_BTT if BTT
help
Memory ranges for PMEM are described by either an NFIT
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 5e019a6942ce..85d4101bb821 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -25,6 +25,8 @@
#include <linux/slab.h>
#include <linux/pmem.h>
#include <linux/nd.h>
+#include <linux/mm.h>
+#include <linux/kmap_pfn.h>
#include "nd.h"

struct pmem_device {
@@ -92,18 +94,12 @@ static int pmem_rw_page(struct block_device *bdev, sector_t sector,
}

static long pmem_direct_access(struct block_device *bdev, sector_t sector,
- void **kaddr, unsigned long *pfn)
+ __pfn_t *pfn)
{
struct pmem_device *pmem = bdev->bd_disk->private_data;
size_t offset = sector << 9;

- if (!pmem)
- return -ENODEV;
-
- /* FIXME convert DAX to comprehend that this mapping has a lifetime */
- *kaddr = (void __force *) pmem->virt_addr + offset;
- *pfn = (pmem->phys_addr + offset) >> PAGE_SHIFT;
-
+ *pfn = phys_to_pfn_t(pmem->phys_addr + offset, PFN_DEV);
return pmem->size - offset;
}

@@ -149,10 +145,17 @@ static void pmem_detach_disk(struct pmem_device *pmem)
blk_cleanup_queue(pmem->pmem_queue);
}

-static int pmem_attach_disk(struct nd_namespace_common *ndns,
+static int pmem_attach_disk(struct device *dev,
+ struct nd_namespace_common *ndns,
struct pmem_device *pmem)
{
struct gendisk *disk;
+ struct resource *res = &(to_nd_namespace_io(&ndns->dev)->res);
+ int err;
+
+ err = devm_register_kmap_pfn_range(dev, res, pmem->virt_addr);
+ if (err)
+ return err;

pmem->pmem_queue = blk_alloc_queue(GFP_KERNEL);
if (!pmem->pmem_queue)
@@ -232,7 +235,8 @@ static int nd_pmem_probe(struct device *dev)
if (nd_btt_probe(ndns, pmem) == 0)
/* we'll come back as btt-pmem */
return -ENXIO;
- return pmem_attach_disk(ndns, pmem);
+
+ return pmem_attach_disk(dev, ndns, pmem);
}

static int nd_pmem_remove(struct device *dev)
diff --git a/drivers/s390/block/Kconfig b/drivers/s390/block/Kconfig
index 4a3b62326183..06c7a1c90d88 100644
--- a/drivers/s390/block/Kconfig
+++ b/drivers/s390/block/Kconfig
@@ -14,6 +14,7 @@ config BLK_DEV_XPRAM

config DCSSBLK
def_tristate m
+ select KMAP_PFN
prompt "DCSSBLK support"
depends on S390 && BLOCK
help
diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
index 2f1734ba0e22..42f1546d7b03 100644
--- a/drivers/s390/block/dcssblk.c
+++ b/drivers/s390/block/dcssblk.c
@@ -16,6 +16,7 @@
#include <linux/blkdev.h>
#include <linux/completion.h>
#include <linux/interrupt.h>
+#include <linux/kmap_pfn.h>
#include <linux/platform_device.h>
#include <asm/extmem.h>
#include <asm/io.h>
@@ -29,7 +30,7 @@ static int dcssblk_open(struct block_device *bdev, fmode_t mode);
static void dcssblk_release(struct gendisk *disk, fmode_t mode);
static void dcssblk_make_request(struct request_queue *q, struct bio *bio);
static long dcssblk_direct_access(struct block_device *bdev, sector_t secnum,
- void **kaddr, unsigned long *pfn);
+ __pfn_t *pfn);

static char dcssblk_segments[DCSSBLK_PARM_LEN] = "\0";

@@ -520,12 +521,18 @@ static const struct attribute_group *dcssblk_dev_attr_groups[] = {
static ssize_t
dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
+ struct resource *res = devm_kzalloc(dev, sizeof(*res), GFP_KERNEL);
int rc, i, j, num_of_segments;
struct dcssblk_dev_info *dev_info;
struct segment_info *seg_info, *temp;
char *local_buf;
unsigned long seg_byte_size;

+ if (!res) {
+ rc = -ENOMEM;
+ goto out_nobuf;
+ }
+
dev_info = NULL;
seg_info = NULL;
if (dev != dcssblk_root_dev) {
@@ -652,6 +659,13 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
if (rc)
goto put_dev;

+ res->start = dev_info->start;
+ res->end = dev_info->end - 1;
+ rc = devm_register_kmap_pfn_range(&dev_info->dev, res,
+ (void *) dev_info->start);
+ if (rc)
+ goto put_dev;
+
get_device(&dev_info->dev);
add_disk(dev_info->gd);

@@ -699,6 +713,8 @@ seg_list_del:
out:
kfree(local_buf);
out_nobuf:
+ if (res)
+ devm_kfree(dev, res);
return rc;
}

@@ -879,7 +895,7 @@ fail:

static long
dcssblk_direct_access (struct block_device *bdev, sector_t secnum,
- void **kaddr, unsigned long *pfn)
+ __pfn_t *pfn)
{
struct dcssblk_dev_info *dev_info;
unsigned long offset, dev_sz;
@@ -889,8 +905,7 @@ dcssblk_direct_access (struct block_device *bdev, sector_t secnum,
return -ENODEV;
dev_sz = dev_info->end - dev_info->start;
offset = secnum * 512;
- *kaddr = (void *) (dev_info->start + offset);
- *pfn = virt_to_phys(*kaddr) >> PAGE_SHIFT;
+ *pfn = phys_to_pfn_t(dev_info->start + offset, PFN_DEV);

return dev_sz - offset;
}
diff --git a/fs/Kconfig b/fs/Kconfig
index 011f43365d7b..bd37234e71a8 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -38,6 +38,7 @@ config FS_DAX
bool "Direct Access (DAX) support"
depends on MMU
depends on !(ARM || MIPS || SPARC)
+ depends on KMAP_PFN
help
Direct Access (DAX) can be used on memory-backed block devices.
If the block device supports DAX and the filesystem supports DAX,
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 3a8ac7edfbf4..73fbc57b6e6d 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -441,7 +441,7 @@ EXPORT_SYMBOL_GPL(bdev_write_page);
* accessible at this address.
*/
long bdev_direct_access(struct block_device *bdev, sector_t sector,
- void **addr, unsigned long *pfn, long size)
+ __pfn_t *pfn, long size)
{
long avail;
const struct block_device_operations *ops = bdev->bd_disk->fops;
@@ -462,7 +462,7 @@ long bdev_direct_access(struct block_device *bdev, sector_t sector,
sector += get_start_sect(bdev);
if (sector % (PAGE_SIZE / 512))
return -EINVAL;
- avail = ops->direct_access(bdev, sector, addr, pfn);
+ avail = ops->direct_access(bdev, sector, pfn);
if (!avail)
return -ERANGE;
return min(avail, size);
diff --git a/fs/dax.c b/fs/dax.c
index c3e21ccfc358..94611f480091 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -26,6 +26,7 @@
#include <linux/sched.h>
#include <linux/uio.h>
#include <linux/vmstat.h>
+#include <linux/kmap_pfn.h>

int dax_clear_blocks(struct inode *inode, sector_t block, long size)
{
@@ -35,13 +36,16 @@ int dax_clear_blocks(struct inode *inode, sector_t block, long size)
might_sleep();
do {
void *addr;
- unsigned long pfn;
+ __pfn_t pfn;
long count;

- count = bdev_direct_access(bdev, sector, &addr, &pfn, size);
+ count = bdev_direct_access(bdev, sector, &pfn, size);
if (count < 0)
return count;
BUG_ON(size < count);
+ addr = kmap_atomic_pfn_t(pfn);
+ if (!addr)
+ return -EIO;
while (count > 0) {
unsigned pgsz = PAGE_SIZE - offset_in_page(addr);
if (pgsz > count)
@@ -57,17 +61,39 @@ int dax_clear_blocks(struct inode *inode, sector_t block, long size)
sector += pgsz / 512;
cond_resched();
}
+ kunmap_atomic_pfn_t(addr);
} while (size);

return 0;
}
EXPORT_SYMBOL_GPL(dax_clear_blocks);

-static long dax_get_addr(struct buffer_head *bh, void **addr, unsigned blkbits)
+static void *__dax_map_bh(struct buffer_head *bh, unsigned blkbits, __pfn_t *pfn)
{
- unsigned long pfn;
sector_t sector = bh->b_blocknr << (blkbits - 9);
- return bdev_direct_access(bh->b_bdev, sector, addr, &pfn, bh->b_size);
+ void *addr;
+ long rc;
+
+ rc = bdev_direct_access(bh->b_bdev, sector, pfn, bh->b_size);
+ if (rc)
+ return ERR_PTR(rc);
+ addr = kmap_atomic_pfn_t(*pfn);
+ if (!addr)
+ return ERR_PTR(-EIO);
+ return addr;
+}
+
+static void *dax_map_bh(struct buffer_head *bh, unsigned blkbits)
+{
+ __pfn_t pfn;
+
+ return __dax_map_bh(bh, blkbits, &pfn);
+}
+
+static void dax_unmap_bh(void *addr)
+{
+ if (!IS_ERR(addr))
+ kunmap_atomic_pfn_t(addr);
}

static void dax_new_buf(void *addr, unsigned size, unsigned first, loff_t pos,
@@ -106,7 +132,7 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
loff_t pos = start;
loff_t max = start;
loff_t bh_max = start;
- void *addr;
+ void *addr = NULL, *kmap = ERR_PTR(-EIO);
bool hole = false;

if (iov_iter_rw(iter) != WRITE)
@@ -142,9 +168,13 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
addr = NULL;
size = bh->b_size - first;
} else {
- retval = dax_get_addr(bh, &addr, blkbits);
- if (retval < 0)
+ dax_unmap_bh(kmap);
+ kmap = dax_map_bh(bh, blkbits);
+ if (IS_ERR(kmap)) {
+ retval = PTR_ERR(kmap);
break;
+ }
+ addr = kmap;
if (buffer_unwritten(bh) || buffer_new(bh))
dax_new_buf(addr, retval, first, pos,
end);
@@ -168,6 +198,8 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
addr += len;
}

+ dax_unmap_bh(kmap);
+
return (pos == start) ? retval : pos - start;
}

@@ -261,11 +293,14 @@ static int copy_user_bh(struct page *to, struct buffer_head *bh,
unsigned blkbits, unsigned long vaddr)
{
void *vfrom, *vto;
- if (dax_get_addr(bh, &vfrom, blkbits) < 0)
- return -EIO;
+
+ vfrom = dax_map_bh(bh, blkbits);
+ if (IS_ERR(vfrom))
+ return PTR_ERR(vfrom);
vto = kmap_atomic(to);
copy_user_page(vto, vfrom, vaddr, to);
kunmap_atomic(vto);
+ dax_unmap_bh(vfrom);
return 0;
}

@@ -273,11 +308,10 @@ static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
struct vm_area_struct *vma, struct vm_fault *vmf)
{
struct address_space *mapping = inode->i_mapping;
- sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
unsigned long vaddr = (unsigned long)vmf->virtual_address;
- void *addr;
- unsigned long pfn;
pgoff_t size;
+ __pfn_t pfn;
+ void *addr;
int error;

i_mmap_lock_read(mapping);
@@ -295,18 +329,17 @@ static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
goto out;
}

- error = bdev_direct_access(bh->b_bdev, sector, &addr, &pfn, bh->b_size);
- if (error < 0)
- goto out;
- if (error < PAGE_SIZE) {
- error = -EIO;
+ addr = __dax_map_bh(bh, inode->i_blkbits, &pfn);
+ if (IS_ERR(addr)) {
+ error = PTR_ERR(addr);
goto out;
}

if (buffer_unwritten(bh) || buffer_new(bh))
clear_page(addr);
+ dax_unmap_bh(addr);

- error = vm_insert_mixed(vma, vaddr, pfn);
+ error = vm_insert_mixed(vma, vaddr, __pfn_t_to_pfn(pfn));

out:
i_mmap_unlock_read(mapping);
@@ -539,10 +572,12 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
return err;
if (buffer_written(&bh)) {
void *addr;
- err = dax_get_addr(&bh, &addr, inode->i_blkbits);
- if (err < 0)
- return err;
+
+ addr = dax_map_bh(&bh, inode->i_blkbits);
+ if (IS_ERR(addr))
+ return PTR_ERR(addr);
memset(addr + offset, 0, length);
+ dax_unmap_bh(addr);
}

return 0;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ff47d5498133..ae59778d8076 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1555,8 +1555,7 @@ struct block_device_operations {
int (*rw_page)(struct block_device *, sector_t, struct page *, int rw);
int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
- long (*direct_access)(struct block_device *, sector_t,
- void **, unsigned long *pfn);
+ long (*direct_access)(struct block_device *, sector_t, __pfn_t *pfn);
unsigned int (*check_events) (struct gendisk *disk,
unsigned int clearing);
/* ->media_changed() is DEPRECATED, use ->check_events() instead */
@@ -1574,8 +1573,8 @@ extern int __blkdev_driver_ioctl(struct block_device *, fmode_t, unsigned int,
extern int bdev_read_page(struct block_device *, sector_t, struct page *);
extern int bdev_write_page(struct block_device *, sector_t, struct page *,
struct writeback_control *);
-extern long bdev_direct_access(struct block_device *, sector_t, void **addr,
- unsigned long *pfn, long size);
+extern long bdev_direct_access(struct block_device *, sector_t,
+ __pfn_t *pfn, long size);
#else /* CONFIG_BLOCK */

struct block_device;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 57ba5ca6be72..c4683ea2fcab 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -951,6 +951,18 @@ enum {
#endif
};

+static inline __pfn_t pfn_to_pfn_t(unsigned long pfn, unsigned long flags)
+{
+ __pfn_t pfn_t = { .val = (pfn << PAGE_SHIFT) | (flags & PFN_MASK), };
+
+ return pfn_t;
+}
+
+static inline __pfn_t phys_to_pfn_t(dma_addr_t addr, unsigned long flags)
+{
+ return pfn_to_pfn_t(addr >> PAGE_SHIFT, flags);
+}
+
static inline bool __pfn_t_has_page(__pfn_t pfn)
{
return (pfn.val & PFN_DEV) == 0;

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