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x86/uaccess: Document copy_from_user_nmi() 

Document the functionality of copy_from_user_nmi() to avoid further
confusion. Fix the typo in the existing comment while at it.

Requested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20201117202753.806376613@linutronix.de
This commit is contained in:
Thomas Gleixner 2020-11-17 21:23:35 +01:00 committed by Borislav Petkov
parent 09a217c105
commit 907f8eb8e0
1 changed files with 18 additions and 4 deletions
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22
arch/x86/lib/usercopy.c
View File

@ -9,9 +9,23 @@
#include <asm/tlbflush.h>
/*
* We rely on the nested NMI work to allow atomic faults from the NMI path; the
* nested NMI paths are careful to preserve CR2.
/**
* copy_from_user_nmi - NMI safe copy from user
* @to: Pointer to the destination buffer
* @from: Pointer to a user space address of the current task
* @n: Number of bytes to copy
*
* Returns: The number of not copied bytes. 0 is success, i.e. all bytes copied
*
* Contrary to other copy_from_user() variants this function can be called
* from NMI context. Despite the name it is not restricted to be called
* from NMI context. It is safe to be called from any other context as
* well. It disables pagefaults across the copy which means a fault will
* abort the copy.
*
* For NMI context invocations this relies on the nested NMI work to allow
* atomic faults from the NMI path; the nested NMI paths are careful to
* preserve CR2.
*/
unsigned long
copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
@ -27,7 +41,7 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
/*
* Even though this function is typically called from NMI/IRQ context
* disable pagefaults so that its behaviour is consistent even when
* called form other contexts.
* called from other contexts.
*/
pagefault_disable();
ret = __copy_from_user_inatomic(to, from, n);