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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 6 Nov 2019 06:45:48 -0000 Received: from d06av21.portsmouth.uk.ibm.com (d06av21.portsmouth.uk.ibm.com [9.149.105.232]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id xA66jk0a48365578 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 6 Nov 2019 06:45:46 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7B7E552054; Wed, 6 Nov 2019 06:45:46 +0000 (GMT) Received: from in.ibm.com (unknown [9.124.35.101]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTPS id 92CD952052; Wed, 6 Nov 2019 06:45:44 +0000 (GMT) Date: Wed, 6 Nov 2019 12:15:42 +0530 From: Bharata B Rao To: Paul Mackerras Subject: Re: [PATCH v10 1/8] mm: ksm: Export ksm_madvise() References: <20191104041800.24527-1-bharata@linux.ibm.com> <20191104041800.24527-2-bharata@linux.ibm.com> <20191106043329.GB12069@oak.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191106043329.GB12069@oak.ozlabs.ibm.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-TM-AS-GCONF: 00 x-cbid: 19110606-0016-0000-0000-000002C123B8 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19110606-0017-0000-0000-000033229DDB Message-Id: <20191106064542.GB21634@in.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-11-06_01:, , 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=733 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1911060070 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: bharata@linux.ibm.com Cc: linuxram@us.ibm.com, cclaudio@linux.ibm.com, kvm-ppc@vger.kernel.org, linux-mm@kvack.org, jglisse@redhat.com, aneesh.kumar@linux.vnet.ibm.com, paulus@au1.ibm.com, sukadev@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org, hch@lst.de Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, Nov 06, 2019 at 03:33:29PM +1100, Paul Mackerras wrote: > On Mon, Nov 04, 2019 at 09:47:53AM +0530, Bharata B Rao wrote: > > KVM PPC module needs ksm_madvise() for supporting secure guests. > > Guest pages that become secure are represented as device private > > pages in the host. Such pages shouldn't participate in KSM merging. > > If we don't do the ksm_madvise call, then as far as I can tell, it > should all still work correctly, but we might have KSM pulling pages > in unnecessarily, causing a reduction in performance. Is that right? I thought so too. When KSM tries to merge a secure page, it should cause a fault resulting in page-out the secure page. However I see the below crash when KSM is enabled and KSM scan tries to kmap and memcmp the device private page. BUG: Unable to handle kernel data access at 0xc007fffe00010000 Faulting instruction address: 0xc0000000000ab5a0 Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Radix MMU=Hash SMP NR_CPUS=2048 NUMA PowerNV Modules linked in: CPU: 0 PID: 22 Comm: ksmd Not tainted 5.4.0-rc2-00026-g2249c0ae4a53-dirty #376 NIP: c0000000000ab5a0 LR: c0000000003d7c3c CTR: 0000000000000004 REGS: c0000001c85d79b0 TRAP: 0300 Not tainted (5.4.0-rc2-00026-g2249c0ae4a53-dirty) MSR: 900000000280b033 CR: 24002242 XER: 20040000 CFAR: c0000000000ab3d0 DAR: c007fffe00010000 DSISR: 40000000 IRQMASK: 0 GPR00: 0000000000000004 c0000001c85d7c40 c0000000018ce000 c0000001c3880000 GPR04: c007fffe00010000 0000000000010000 0000000000000000 ffffffffffffffff GPR08: c000000001992298 0000603820002138 ffffffffffffffff ffffffff00003a69 GPR12: 0000000024002242 c000000002550000 c0000001c8700000 c00000000179b728 GPR16: c00c01ffff800040 c00000000179b5b8 c00c00000070e200 ffffffffffffffff GPR20: 0000000000000000 0000000000000000 fffffffffffff000 c00000000179b648 GPR24: c0000000024464a0 c00000000249f568 c000000001118918 0000000000000000 GPR28: c0000001c804c590 c00000000249f518 0000000000000000 c0000001c8700000 NIP [c0000000000ab5a0] memcmp+0x320/0x6a0 LR [c0000000003d7c3c] memcmp_pages+0x8c/0xe0 Call Trace: [c0000001c85d7c40] [c0000001c804c590] 0xc0000001c804c590 (unreliable) [c0000001c85d7c70] [c0000000004591d0] ksm_scan_thread+0x960/0x21b0 [c0000001c85d7db0] [c0000000001bf328] kthread+0x198/0x1a0 [c0000001c85d7e20] [c00000000000bfbc] ret_from_kernel_thread+0x5c/0x80 Instruction dump: ebc1fff0 eba1ffe8 eb81ffe0 eb61ffd8 4e800020 38600001 4d810020 3860ffff 4e800020 38000004 7c0903a6 7d201c28 <7d402428> 7c295040 38630008 38840008 In anycase, we wouldn't want secure guests pages to be pulled out due to KSM, hence disabled merging. Regards, Bharata.