From: Oleg Nesterov Subject: Re: [PATCH v2] x86: make DR*_RESERVED unsigned long Date: Sat, 27 Apr 2013 16:45:37 +0200 Message-ID: <20130427144537.GA24256@redhat.com> References: <20130424072630.GB1780@gmail.com> <20130424170702.GA1867@redhat.com> <5178282D.9030902@zytor.com> <20130425144818.GA25921@redhat.com> <20130426163802.GA30351@redhat.com> <517AAED5.7040400@zytor.com> <20130426171526.GA30875@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ingo Molnar , Linus Torvalds , Cyrill Gorcunov , Peter Zijlstra , Thomas Gleixner , David Miller , "Theodore Ts'o" , Linux Kernel Mailing List , the arch/x86 maintainers , Network Development , "linux-ext4@vger.kernel.org" , Fr??d??ric Weisbecker To: "H. Peter Anvin" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:20317 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754105Ab3D0Osw (ORCPT ); Sat, 27 Apr 2013 10:48:52 -0400 Content-Disposition: inline In-Reply-To: <20130426171526.GA30875@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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 */ #define DR_TRAP0 (0x1) /* db0 */ #define DR_TRAP1 (0x2) /* db1 */ @@ -32,6 +31,8 @@ and indicates what types of access we trap on, and how large the data field is that we are looking at */ +#define DR_CONTROL_MASK (0xFFFF03FFU) /* Everything else is reserved */ + #define DR_CONTROL_SHIFT 16 /* Skip this many bits in ctl register */ #define DR_CONTROL_SIZE 4 /* 4 control bits per register */ @@ -64,12 +65,6 @@ 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 */ -#else -#define DR_CONTROL_RESERVED (0xFFFFFFFF0000FC00UL) /* Reserved */ -#endif - #define DR_LOCAL_SLOWDOWN (0x100) /* Local slow the pipeline */ #define DR_GLOBAL_SLOWDOWN (0x200) /* Global slow the pipeline */ diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 7461f50..bc5fb98 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -657,7 +657,7 @@ static int ptrace_write_dr7(struct task_struct *tsk, unsigned long data) bool second_pass = false; int i, rc, ret = 0; - data &= ~DR_CONTROL_RESERVED; + data &= DR_CONTROL_MASK; old_dr7 = ptrace_get_dr7(thread->ptrace_bps); restore: diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 68bda7a..42a635f 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -402,7 +402,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code) get_debugreg(dr6, 6); /* Filter out all the reserved bits which are preset to 1 */ - dr6 &= ~DR6_RESERVED; + dr6 &= DR6_MASK; /* * If dr6 has no reason to give us about the origin of this trap,