Re: [PATCH v2] x86: make DR*_RESERVED unsigned long

From: Oleg Nesterov
Date: Fri Apr 26 2013 - 13:18:45 EST

On 04/26, H. Peter Anvin wrote:
> On 04/26/2013 09:38 AM, Oleg Nesterov wrote:
> >
> > - 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.

OK, I meant that it also clears the bits that are not specified in

> 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.

Then we should do

- #define DR6_RESERVED 0xFFFF0FF0


or what? (just in case, I will happily agree with "do nothing" ;)

> The comment should probably be corrected, though.

Which one?

/* Define reserved bits in DR6 which are always set to 1 */

/* Filter out all the reserved bits which are preset to 1 */
dr6 &= ~DR6_RESERVED;

I guess both should be updated then. But if I read the doc correctly
the lower reserved bits are set to 1.

However do_debug() does set_debugreg(0, 6) and this looks correct, the
doc says "debug handlers should clear the register before returning to
the interrupted task".


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at