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

From: Oleg Nesterov
Date: Sun Apr 28 2013 - 13:30:57 EST

On 04/28, Frederic Weisbecker wrote:
> On Sat, Apr 27, 2013 at 04:45:37PM +0200, Oleg Nesterov wrote:
> >
> > -/* Define reserved bits in DR6 which are always set to 1 */
> > -#define DR6_RESERVED (0xFFFF0FF0)
> > +#define DR6_MASK (0xF00FU) /* Everything else is reserved */
> I'm personally fine either with that or with Peter's suggestion to do:
> -#define DR6_RESERVED (0xFFFF0FF0)
> +#define DR6_RESERVED (~0xF00FUL)

I missed this suggestion...

Yes, and this allows to kill ifdef too.

> If this should stay stable UAPI,

I do not know, but I guess it would be safer to keep the old define's.

> I really don't mind.

Oh, I do not mind too ;)

OK, please see v3.

Subject: [PATCH v3] x86: make DR*_RESERVED unsigned long

DR6_RESERVED and DR_CONTROL_RESERVED are used to clear the unwanted
bits in the "unsigned long" data, but "ulong &= ~int" also clears the
upper bits that are not specified in mask.

This is actually fine, dr6[32:63] are reserved, but this is not clear
so it would be better to make them "unsigned long" to cleanup the code.

However, depending on sizeof(long), DR6_RESERVED should be either
0xFFFF0FF0 or 0xFFFFFFFF_FFFF0FF0, so this patch redefines them as
(~ 32_bit_mask UL) to avoid ifdef's.

Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Suggested-by: H. Peter Anvin <hpa@xxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
arch/x86/include/uapi/asm/debugreg.h | 8 ++------
1 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/uapi/asm/debugreg.h b/arch/x86/include/uapi/asm/debugreg.h
index 3c0874d..4ff5d05 100644
--- a/arch/x86/include/uapi/asm/debugreg.h
+++ b/arch/x86/include/uapi/asm/debugreg.h
@@ -15,7 +15,7 @@
are either reserved or not of interest to us. */

/* Define reserved bits in DR6 which are always set to 1 */
-#define DR6_RESERVED (0xFFFF0FF0)
+#define DR6_RESERVED (~0xF00FUL)

#define DR_TRAP0 (0x1) /* db0 */
#define DR_TRAP1 (0x2) /* db1 */
@@ -64,11 +64,7 @@
We can slow the instruction pipeline for instructions coming via the
gdt or the ldt if we want to. I am not sure why this is an advantage */

-#ifdef __i386__
-#define DR_CONTROL_RESERVED (0xFC00) /* Reserved by Intel */
-#define DR_CONTROL_RESERVED (0xFFFFFFFF0000FC00UL) /* Reserved */
+#define DR_CONTROL_RESERVED (~0xFFFF03FFUL) /* Reserved by Intel */

#define DR_LOCAL_SLOWDOWN (0x100) /* Local slow the pipeline */
#define DR_GLOBAL_SLOWDOWN (0x200) /* Global slow the pipeline */

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