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Message-Id: <20210804043231.2655537-17-ira.weiny@intel.com>
Date: Tue, 3 Aug 2021 21:32:29 -0700
From: ira.weiny@...el.com
To: Dave Hansen <dave.hansen@...ux.intel.com>,
Dan Williams <dan.j.williams@...el.com>
Cc: Ira Weiny <ira.weiny@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Peter Zijlstra <peterz@...radead.org>,
Andy Lutomirski <luto@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
Fenghua Yu <fenghua.yu@...el.com>,
Rick Edgecombe <rick.p.edgecombe@...el.com>, x86@...nel.org,
linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev,
linux-mm@...ck.org
Subject: [PATCH V7 16/18] dax: Stray access protection for dax_direct_access()
From: Ira Weiny <ira.weiny@...el.com>
dax_direct_access() provides a way to obtain the direct map address of
PMEM memory. Coordinate PKS protection with dax_direct_access() of
protected devmap pages.
Introduce 3 new calls dax_{protected,mk_readwrite,mk_noaccess}()
These 3 calls do not have to be implemented by the dax provider if no
protection is implemented.
Single threads of execution can use dax_mk_{readwrite,noaccess}() to
relax the protection of the dax device and allow direct use of the kaddr
returned from dax_direct_access(). dax_mk_{readwrite,noaccess}() must
be used within the dax_read_[un]lock() protected region. And they only
need to be used to guard actual access to the memory pointed to. Other
uses of dax_direct_access() do not need to use these guards.
For users who require a permanent address to the dax device such as the
DM write cache. dax_protected() indicates that the dax device has
additional protections. In this case the user choses to create it's own
mapping of the memory.
Signed-off-by: Ira Weiny <ira.weiny@...el.com>
---
Changes for V7
Rework cover letter.
Do not include a FS_DAX_LIMITED restriction for dcss. It will
simply not implement the protection and there is no need
to special case this.
Clean up commit message because I did not originally
understand the nuance of the s390 device.
Introduce dax_{protected,mk_readwrite,mk_noaccess}()
From Dan Williams
Remove old clean up cruft from previous versions
Remove map_protected
Remove 'global' parameters all calls
---
drivers/dax/super.c | 54 ++++++++++++++++++++++++++++++++++++++
drivers/md/dm-writecache.c | 8 +++++-
fs/dax.c | 8 ++++++
fs/fuse/virtio_fs.c | 2 ++
include/linux/dax.h | 8 ++++++
5 files changed, 79 insertions(+), 1 deletion(-)
diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 44736cbd446e..dc05c89102d0 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -296,6 +296,8 @@ EXPORT_SYMBOL_GPL(dax_attribute_group);
* @pgoff: offset in pages from the start of the device to translate
* @nr_pages: number of consecutive pages caller can handle relative to @pfn
* @kaddr: output parameter that returns a virtual address mapping of pfn
+ * Direct access through this pointer must be guarded by calls to
+ * dax_mk_{readwrite,noaccess}()
* @pfn: output parameter that returns an absolute pfn translation of @pgoff
*
* Return: negative errno if an error occurs, otherwise the number of
@@ -389,6 +391,58 @@ void dax_flush(struct dax_device *dax_dev, void *addr, size_t size)
#endif
EXPORT_SYMBOL_GPL(dax_flush);
+bool dax_map_protected(struct dax_device *dax_dev)
+{
+ if (!dax_alive(dax_dev))
+ return false;
+
+ if (dax_dev->ops->map_protected)
+ return dax_dev->ops->map_protected(dax_dev);
+ return false;
+}
+EXPORT_SYMBOL_GPL(dax_map_protected);
+
+/**
+ * dax_mk_readwrite() - make protected dax devices read/write
+ * @dax_dev: the dax device representing the memory to access
+ *
+ * Any access of the kaddr memory returned from dax_direct_access() must be
+ * guarded by dax_mk_readwrite() and dax_mk_noaccess(). This ensures that any
+ * dax devices which have additional protections are allowed to relax those
+ * protections for the thread using this memory.
+ *
+ * NOTE these calls must be contained within a single thread of execution and
+ * both must be guarded by dax_read_lock() Which is also a requirement for
+ * dax_direct_access() anyway.
+ */
+void dax_mk_readwrite(struct dax_device *dax_dev)
+{
+ if (!dax_alive(dax_dev))
+ return;
+
+ if (dax_dev->ops->mk_readwrite)
+ dax_dev->ops->mk_readwrite(dax_dev);
+}
+EXPORT_SYMBOL_GPL(dax_mk_readwrite);
+
+/**
+ * dax_mk_noaccess() - restore protection to dax devices if needed
+ * @dax_dev: the dax device representing the memory to access
+ *
+ * See dax_direct_access() and dax_mk_readwrite()
+ *
+ * NOTE Must be called prior to dax_read_unlock()
+ */
+void dax_mk_noaccess(struct dax_device *dax_dev)
+{
+ if (!dax_alive(dax_dev))
+ return;
+
+ if (dax_dev->ops->mk_noaccess)
+ dax_dev->ops->mk_noaccess(dax_dev);
+}
+EXPORT_SYMBOL_GPL(dax_mk_noaccess);
+
void dax_write_cache(struct dax_device *dax_dev, bool wc)
{
if (wc)
diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index e21e29e81bbf..27671300ad50 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -284,7 +284,13 @@ static int persistent_memory_claim(struct dm_writecache *wc)
r = -EOPNOTSUPP;
goto err2;
}
- if (da != p) {
+
+ /*
+ * Force the write cache to map the pages directly if the dax device
+ * mapping is protected or if the number of pages returned was not what
+ * was requested.
+ */
+ if (dax_map_protected(wc->ssd_dev->dax_dev) || da != p) {
long i;
wc->memory_map = NULL;
pages = kvmalloc_array(p, sizeof(struct page *), GFP_KERNEL);
diff --git a/fs/dax.c b/fs/dax.c
index 99b4e78d888f..9dfb93b39754 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -728,7 +728,9 @@ static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_d
return rc;
}
vto = kmap_atomic(to);
+ dax_mk_readwrite(dax_dev);
copy_user_page(vto, (void __force *)kaddr, vaddr, to);
+ dax_mk_noaccess(dax_dev);
kunmap_atomic(vto);
dax_read_unlock(id);
return 0;
@@ -1096,8 +1098,10 @@ s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
}
if (!page_aligned) {
+ dax_mk_readwrite(iomap->dax_dev);
memset(kaddr + offset, 0, size);
dax_flush(iomap->dax_dev, kaddr + offset, size);
+ dax_mk_noaccess(iomap->dax_dev);
}
dax_read_unlock(id);
return size;
@@ -1169,6 +1173,8 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
if (map_len > end - pos)
map_len = end - pos;
+ dax_mk_readwrite(dax_dev);
+
/*
* The userspace address for the memory copy has already been
* validated via access_ok() in either vfs_read() or
@@ -1181,6 +1187,8 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
xfer = dax_copy_to_iter(dax_dev, pgoff, kaddr,
map_len, iter);
+ dax_mk_noaccess(dax_dev);
+
pos += xfer;
length -= xfer;
done += xfer;
diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 8f52cdaa8445..3dfb053b1c4d 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -776,8 +776,10 @@ static int virtio_fs_zero_page_range(struct dax_device *dax_dev,
rc = dax_direct_access(dax_dev, pgoff, nr_pages, &kaddr, NULL);
if (rc < 0)
return rc;
+ dax_mk_readwrite(dax_dev);
memset(kaddr, 0, nr_pages << PAGE_SHIFT);
dax_flush(dax_dev, kaddr, nr_pages << PAGE_SHIFT);
+ dax_mk_noaccess(dax_dev);
return 0;
}
diff --git a/include/linux/dax.h b/include/linux/dax.h
index b52f084aa643..8ad4839705ca 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -36,6 +36,10 @@ struct dax_operations {
struct iov_iter *);
/* zero_page_range: required operation. Zero page range */
int (*zero_page_range)(struct dax_device *, pgoff_t, size_t);
+
+ bool (*map_protected)(struct dax_device *dax_dev);
+ void (*mk_readwrite)(struct dax_device *dax_dev);
+ void (*mk_noaccess)(struct dax_device *dax_dev);
};
extern struct attribute_group dax_attribute_group;
@@ -228,6 +232,10 @@ int dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff,
size_t nr_pages);
void dax_flush(struct dax_device *dax_dev, void *addr, size_t size);
+bool dax_map_protected(struct dax_device *dax_dev);
+void dax_mk_readwrite(struct dax_device *dax_dev);
+void dax_mk_noaccess(struct dax_device *dax_dev);
+
ssize_t dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
const struct iomap_ops *ops);
vm_fault_t dax_iomap_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
--
2.28.0.rc0.12.gb6a658bd00c9
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