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Commit ce37defc authored by Borislav Petkov's avatar Borislav Petkov
Browse files

x86: Document rdmsr_safe restrictions 

Recently, I got bitten by using rdmsr_safe too early in the boot
process. Document its shortcomings for future reference.

Link: http://lkml.kernel.org/r/4ED5B70F.606@lwfinger.net


Signed-off-by: default avatarBorislav Petkov <borislav.petkov@amd.com>
parent bd399063

arch/x86/include/asm/msr.h

+8 −1
Original line number Diff line number Diff line
@@ -169,7 +169,14 @@ static inline int wrmsr_safe(unsigned msr, unsigned low, unsigned high) 
	return native_write_msr_safe(msr, low, high);

}



/* rdmsr with exception handling */

/*

 * rdmsr with exception handling.

 *

 * Please note that the exception handling works only after we've

 * switched to the "smart" #GP handler in trap_init() which knows about

 * exception tables - using this macro earlier than that causes machine

 * hangs on boxes which do not implement the @msr in the first argument.

 */

#define rdmsr_safe(msr, p1, p2)					\

({								\

	int __err;						\