From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A66ADC5DF61 for ; Thu, 7 Nov 2019 05:45:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 33F32214D8 for ; Thu, 7 Nov 2019 05:45:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ozlabs.org header.i=@ozlabs.org header.b="btTM+JO9" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 33F32214D8 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ozlabs.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 908936B0003; Thu, 7 Nov 2019 00:45:47 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 8B92D6B0006; Thu, 7 Nov 2019 00:45:47 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7CF2A6B0007; Thu, 7 Nov 2019 00:45:47 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0212.hostedemail.com [216.40.44.212]) by kanga.kvack.org (Postfix) with ESMTP id 69E986B0003 for ; Thu, 7 Nov 2019 00:45:47 -0500 (EST) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id EE2772C88 for ; Thu, 7 Nov 2019 05:45:46 +0000 (UTC) X-FDA: 76128394692.09.bulb72_4f7185ed28a3f X-HE-Tag: bulb72_4f7185ed28a3f X-Filterd-Recvd-Size: 4938 Received: from ozlabs.org (ozlabs.org [203.11.71.1]) by imf39.hostedemail.com (Postfix) with ESMTP for ; Thu, 7 Nov 2019 05:45:45 +0000 (UTC) Received: by ozlabs.org (Postfix, from userid 1003) id 477snc6KMbz9sWx; Thu, 7 Nov 2019 16:45:40 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ozlabs.org; s=201707; t=1573105540; bh=v04gpqPuQsMYJe1XTEi01nFH99poTytMgQDqvHAql10=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=btTM+JO9ec0tnAra1rxspTAzuX4dmHSwx5F3iPKpRDE1Dyy7H2lCI89oVQBvfAAQ6 ur1klG5Ekm5jzpUWTLAyOyJfJYPs4n1XrxybuX7LMqvepoNxTZMhhRZjboNtJJLraS L3rUCeqJ/N28fmgLbr+39yfvgI3hDzdJJEeHAEzXTsWT67aUSTjT2TrM9FRmsb2ZX+ Dz+9847F24kuYlHhFHYRBvoYF5KLRww2/hDpxO5JiiYWtSEecVc8c34OzzZdGNegYn v0ZcRc24HBfiQUQXgmKhdq5Xpou5e2aLTaQ7WnAZ4YuiA/kofjJz6JiuTee/DVEPZ2 FauPmtkkfgc8g== Date: Thu, 7 Nov 2019 16:45:35 +1100 From: Paul Mackerras To: Bharata B Rao Cc: linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, linux-mm@kvack.org, paulus@au1.ibm.com, aneesh.kumar@linux.vnet.ibm.com, jglisse@redhat.com, cclaudio@linux.ibm.com, linuxram@us.ibm.com, sukadev@linux.vnet.ibm.com, hch@lst.de Subject: Re: [PATCH v10 1/8] mm: ksm: Export ksm_madvise() Message-ID: <20191107054535.GA2882@oak.ozlabs.ibm.com> References: <20191104041800.24527-1-bharata@linux.ibm.com> <20191104041800.24527-2-bharata@linux.ibm.com> <20191106043329.GB12069@oak.ozlabs.ibm.com> <20191106064542.GB21634@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191106064542.GB21634@in.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Nov 06, 2019 at 12:15:42PM +0530, Bharata B Rao wrote: > 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 Hmmm, that seems like a bug in the ZONE_DEVICE stuff generally. All that ksm is doing as far as I can see is follow_page() and kmap_atomic(). I wonder how many other places in the kernel might also be prone to crashing if they try to touch device pages? > In anycase, we wouldn't want secure guests pages to be pulled out due > to KSM, hence disabled merging. Sure, I don't disagree with that, but I worry that we are papering over a bug here. Paul. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 21BFFC5DF61 for ; Thu, 7 Nov 2019 08:00:13 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id AB8BF21D7E for ; Thu, 7 Nov 2019 08:00:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=ozlabs.org header.i=@ozlabs.org header.b="btTM+JO9" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB8BF21D7E Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=ozlabs.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 477wmp62DFzF3DD for ; Thu, 7 Nov 2019 19:00:10 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 477wd72sTHzF15Z for ; Thu, 7 Nov 2019 18:53:31 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=ozlabs.org Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; secure) header.d=ozlabs.org header.i=@ozlabs.org header.b="btTM+JO9"; dkim-atps=neutral Received: by ozlabs.org (Postfix, from userid 1003) id 477snc6KMbz9sWx; Thu, 7 Nov 2019 16:45:40 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ozlabs.org; s=201707; t=1573105540; bh=v04gpqPuQsMYJe1XTEi01nFH99poTytMgQDqvHAql10=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=btTM+JO9ec0tnAra1rxspTAzuX4dmHSwx5F3iPKpRDE1Dyy7H2lCI89oVQBvfAAQ6 ur1klG5Ekm5jzpUWTLAyOyJfJYPs4n1XrxybuX7LMqvepoNxTZMhhRZjboNtJJLraS L3rUCeqJ/N28fmgLbr+39yfvgI3hDzdJJEeHAEzXTsWT67aUSTjT2TrM9FRmsb2ZX+ Dz+9847F24kuYlHhFHYRBvoYF5KLRww2/hDpxO5JiiYWtSEecVc8c34OzzZdGNegYn v0ZcRc24HBfiQUQXgmKhdq5Xpou5e2aLTaQ7WnAZ4YuiA/kofjJz6JiuTee/DVEPZ2 FauPmtkkfgc8g== Date: Thu, 7 Nov 2019 16:45:35 +1100 From: Paul Mackerras To: Bharata B Rao Subject: Re: [PATCH v10 1/8] mm: ksm: Export ksm_madvise() Message-ID: <20191107054535.GA2882@oak.ozlabs.ibm.com> References: <20191104041800.24527-1-bharata@linux.ibm.com> <20191104041800.24527-2-bharata@linux.ibm.com> <20191106043329.GB12069@oak.ozlabs.ibm.com> <20191106064542.GB21634@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191106064542.GB21634@in.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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: , 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 12:15:42PM +0530, Bharata B Rao wrote: > 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 Hmmm, that seems like a bug in the ZONE_DEVICE stuff generally. All that ksm is doing as far as I can see is follow_page() and kmap_atomic(). I wonder how many other places in the kernel might also be prone to crashing if they try to touch device pages? > In anycase, we wouldn't want secure guests pages to be pulled out due > to KSM, hence disabled merging. Sure, I don't disagree with that, but I worry that we are papering over a bug here. Paul. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Mackerras Date: Thu, 07 Nov 2019 05:45:35 +0000 Subject: Re: [PATCH v10 1/8] mm: ksm: Export ksm_madvise() Message-Id: <20191107054535.GA2882@oak.ozlabs.ibm.com> List-Id: References: <20191104041800.24527-1-bharata@linux.ibm.com> <20191104041800.24527-2-bharata@linux.ibm.com> <20191106043329.GB12069@oak.ozlabs.ibm.com> <20191106064542.GB21634@in.ibm.com> In-Reply-To: <20191106064542.GB21634@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Bharata B Rao Cc: linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, linux-mm@kvack.org, paulus@au1.ibm.com, aneesh.kumar@linux.vnet.ibm.com, jglisse@redhat.com, cclaudio@linux.ibm.com, linuxram@us.ibm.com, sukadev@linux.vnet.ibm.com, hch@lst.de On Wed, Nov 06, 2019 at 12:15:42PM +0530, Bharata B Rao wrote: > 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_SIZEdK MMU=Radix MMU=Hash SMP NR_CPUS 48 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 Hmmm, that seems like a bug in the ZONE_DEVICE stuff generally. All that ksm is doing as far as I can see is follow_page() and kmap_atomic(). I wonder how many other places in the kernel might also be prone to crashing if they try to touch device pages? > In anycase, we wouldn't want secure guests pages to be pulled out due > to KSM, hence disabled merging. Sure, I don't disagree with that, but I worry that we are papering over a bug here. Paul.