linux-kernel - [PATCH 1/2] x86: Add a __copy_from_user

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Date:	Mon, 16 Nov 2015 15:23:02 -0800
From:	Andi Kleen <andi@...stfloor.org>
To:	peterz@...radead.org
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH 1/2] x86: Add a __copy_from_user_nmi

From: Andi Kleen <ak@...ux.intel.com>

Add a inlined __ variant of copy_from_user_nmi. The inlined variant allows
the user to:

- batch the access_ok check for multiple accesses
- avoid having a pagefault_disable/enable on every access if the caller
already ensures disabled page faults due to its context.
- get all the optimizations in copy_*_user for small constant sized transfers

It is just a define to __copy_from_user_inatomic.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/include/asm/uaccess.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index a8df874..1d0766c 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -745,5 +745,14 @@ copy_to_user(void __user *to, const void *from, unsigned long n)
 #undef __copy_from_user_overflow
 #undef __copy_to_user_overflow
 
+/*
+ * We rely on the nested NMI work to allow atomic faults from the NMI path; the
+ * nested NMI paths are careful to preserve CR2.
+ *
+ * Caller must use pagefault_enable/disable, or run in interrupt context,
+ * and also do a uaccess_ok() check
+ */
+#define __copy_from_user_nmi __copy_from_user_inatomic
+
 #endif /* _ASM_X86_UACCESS_H */
 
-- 
2.4.3

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