[tip:perf/core] x86: Add an inlined __copy_from_user_nmi() variant

[tip-bot for Andi Kleen]

Commit-ID:  10013ebb5d7856c243541870f4e62fed68253e88
Gitweb:     http://git.kernel.org/tip/10013ebb5d7856c243541870f4e62fed68253e88
Author:     Andi Kleen <ak@xxxxxxxxxxxxxxx>
AuthorDate: Thu, 22 Oct 2015 15:07:20 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 23 Nov 2015 09:58:24 +0100

x86: Add an inlined __copy_from_user_nmi() variant

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@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1445551641-13379-1-git-send-email-andi@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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 09b1b0a..660458a 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 */
 
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