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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 4 Sep 2019 15:42:37 +0100 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x84Ega2d43647078 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 4 Sep 2019 14:42:36 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A214EAE055; Wed, 4 Sep 2019 14:42:36 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 349A4AE045; Wed, 4 Sep 2019 14:42:36 +0000 (GMT) Received: from localhost (unknown [9.199.56.52]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 4 Sep 2019 14:42:36 +0000 (GMT) Date: Wed, 04 Sep 2019 20:12:34 +0530 From: "Naveen N. Rao" Subject: Re: [PATCH v3 2/3] Powerpc64/Watchpoint: Don't ignore extraneous exceptions To: mikey@neuling.org, mpe@ellerman.id.au, Ravi Bangoria Cc: benh@kernel.crashing.org, christophe.leroy@c-s.fr, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, npiggin@gmail.com, paulus@samba.org References: <20190710045445.31037-1-ravi.bangoria@linux.ibm.com> <20190710045445.31037-3-ravi.bangoria@linux.ibm.com> In-Reply-To: <20190710045445.31037-3-ravi.bangoria@linux.ibm.com> MIME-Version: 1.0 User-Agent: astroid/0.15.0 (https://github.com/astroidmail/astroid) Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8BIT X-TM-AS-GCONF: 00 x-cbid: 19090414-0028-0000-0000-00000397A571 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19090414-0029-0000-0000-00002459F765 Message-Id: <1567608022.j44gajn34z.naveen@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-09-04_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=921 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1909040143 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ravi Bangoria wrote: > On Powerpc64, watchpoint match range is double-word granular. On > a watchpoint hit, DAR is set to the first byte of overlap between > actual access and watched range. And thus it's quite possible that > DAR does not point inside user specified range. Ex, say user creates > a watchpoint with address range 0x1004 to 0x1007. So hw would be > configured to watch from 0x1000 to 0x1007. If there is a 4 byte > access from 0x1002 to 0x1005, DAR will point to 0x1002 and thus > interrupt handler considers it as extraneous, but it's actually not, > because part of the access belongs to what user has asked. So, let > kernel pass it on to user and let user decide what to do with it > instead of silently ignoring it. The drawback is, it can generate > false positive events. I think you should do the additional validation here, instead of generating false positives. You should be able to read the instruction, run it through analyse_instr(), and then use OP_IS_LOAD_STORE() and GETSIZE() to understand the access range. This can be used to then perform a better match against what the user asked for. - Naveen