Messages in this thread | | | Date | Fri, 26 Apr 2013 09:44:05 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH v2] x86: make DR*_RESERVED unsigned long |
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On 04/26/2013 09:38 AM, Oleg Nesterov wrote: > DR6_RESERVED and DR_CONTROL_RESERVED are used to clear the set > bits in the "unsigned long" data, make them long to ensure that > "&~" doesn't clear the upper bits. > > This is only cleanup, the usage of ~DR*_RESERVED is safe but > doesn't look clean and the pattern is error prone. > > - do_debug: > > dr6 &= ~DR6_RESERVED; > > this also wrongly clears 32-63 bits. Fortunately these > bits are reserved and must be zero. >
I don't think this is wrongly at all. The whole point is to mask out the bits that the handler doesn't want to deal with, so masking out the reserved bits [63:32] seems reasonable to me.
The comment should probably be corrected, though.
-hpa
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