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Message-ID: <20130428005814.GB10354@somewhere>
Date: Sun, 28 Apr 2013 02:58:16 +0200
From: Frederic Weisbecker <fweisbec@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Cyrill Gorcunov <gorcunov@...il.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Thomas Gleixner <tglx@...utronix.de>,
David Miller <davem@...emloft.net>,
Theodore Ts'o <tytso@....edu>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
the arch/x86 maintainers <x86@...nel.org>,
Network Development <netdev@...r.kernel.org>,
"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2] x86: make DR*_RESERVED unsigned long
On Sat, Apr 27, 2013 at 04:45:37PM +0200, Oleg Nesterov wrote:
> On 04/26, Oleg Nesterov wrote:
>
> > 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
> > DR6_RESERVED mask.
> >
> > > 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
> > + #define DR6_RESERVED 0xFFFFFFFFFFFF0FF0
> >
> > ?
> >
> > or what? (just in case, I will happily agree with "do nothing" ;)
>
> Or we can do the s/reserved/mask/ change and avoid any "unexpected"
> effect of "long &= ~int". This allso allows to kill ifdef(__i386__).
>
> But this is include/uapi, I do not know if I can simply remove the
> old define's.
>
> In short: whatever you prefer, including "leave it alone".
>
> Oleg.
>
> diff --git a/arch/x86/include/uapi/asm/debugreg.h b/arch/x86/include/uapi/asm/debugreg.h
> index 3c0874d..2678b23 100644
> --- a/arch/x86/include/uapi/asm/debugreg.h
> +++ b/arch/x86/include/uapi/asm/debugreg.h
> @@ -14,8 +14,7 @@
> which debugging register was responsible for the trap. The other bits
> 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_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)
If this should stay stable UAPI, we probably want Peter's solution. Otherwise
I really don't mind.
Thanks.
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