Messages in this thread Patch in this message | | | Date | Mon, 5 Dec 2011 09:40:30 -0800 | From | tip-bot for Borislav Petkov <> | Subject | [tip:x86/urgent] x86: Document rdmsr_safe restrictions |
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Commit-ID: ce37defc0f6673f5ca2c92ed5cfcaf290ae7dd16 Gitweb: http://git.kernel.org/tip/ce37defc0f6673f5ca2c92ed5cfcaf290ae7dd16 Author: Borislav Petkov <borislav.petkov@amd.com> AuthorDate: Mon, 5 Dec 2011 14:28:37 +0100 Committer: Borislav Petkov <borislav.petkov@amd.com> CommitDate: Mon, 5 Dec 2011 14:28:37 +0100
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: Borislav Petkov <borislav.petkov@amd.com> --- arch/x86/include/asm/msr.h | 9 ++++++++- 1 files changed, 8 insertions(+), 1 deletions(-)
diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h index 084ef95..95203d4 100644 --- a/arch/x86/include/asm/msr.h +++ b/arch/x86/include/asm/msr.h @@ -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; \
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