[RFC PATCH 13/15] dax: Stray write protection for dax_direct_access()

ira.weiny
2020-07-14T07:04:32Z

From: Ira Weiny <ira.weiny@intel.com>

dax_direct_access() is a special case of accessing pmem via a page
offset and without a struct page.

Because the dax driver is well aware of the special protections it has
mapped memory with, call dev_access_[en|dis]able() directly instead of
the unnecessary overhead of trying to get a page to kmap.

Like kmap though, leverage the existing dax_read[un]lock() functions
because they are already required to surround the use of the memory
returned from dax_direct_access().

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
---
drivers/dax/super.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 021739768093..e8d0a28e6ed2 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -30,12 +30,14 @@ static DEFINE_SPINLOCK(dax_host_lock);

int dax_read_lock(void)
{
+ dev_access_enable();
return srcu_read_lock(&dax_srcu);
}
EXPORT_SYMBOL_GPL(dax_read_lock);

void dax_read_unlock(int id)
{
+ dev_access_disable();
srcu_read_unlock(&dax_srcu, id);
}
EXPORT_SYMBOL_GPL(dax_read_unlock);