linux-kernel - [RFC PATCH 13/15] dax: Stray write protection for dax_direct

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Message-Id: <20200714070220.3500839-14-ira.weiny@intel.com>
Date:   Tue, 14 Jul 2020 00:02:18 -0700
From:   ira.weiny@...el.com
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Ira Weiny <ira.weiny@...el.com>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: [RFC PATCH 13/15] dax: Stray write protection for dax_direct_access()

From: Ira Weiny <ira.weiny@...el.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@...el.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);
-- 
2.25.1