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[35.233.69.230]) by smtp.gmail.com with ESMTPSA id r10sm7196657wmh.45.2021.03.03.03.09.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Mar 2021 03:09:01 -0800 (PST) Date: Wed, 3 Mar 2021 11:08:56 +0000 From: Quentin Perret To: Marc Zyngier Subject: Re: [PATCH] KVM: arm64: Fix unaligned addr case in mmu walking Message-ID: References: <20210303024225.2591-1-justin.he@arm.com> <87sg5czhny.wl-maz@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <87sg5czhny.wl-maz@kernel.org> Cc: Jia He , Catalin Marinas , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Will Deacon , kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Wednesday 03 Mar 2021 at 09:54:25 (+0000), Marc Zyngier wrote: > Hi Jia, > > On Wed, 03 Mar 2021 02:42:25 +0000, > Jia He wrote: > > > > If the start addr is not aligned with the granule size of that level. > > loop step size should be adjusted to boundary instead of simple > > kvm_granual_size(level) increment. Otherwise, some mmu entries might miss > > the chance to be walked through. > > E.g. Assume the unmap range [data->addr, data->end] is > > [0xff00ab2000,0xff00cb2000] in level 2 walking and NOT block mapping. > > When does this occur? Upgrade from page mappings to block? Swap out? > > > And the 1st part of that pmd entry is [0xff00ab2000,0xff00c00000]. The > > pmd value is 0x83fbd2c1002 (not valid entry). In this case, data->addr > > should be adjusted to 0xff00c00000 instead of 0xff00cb2000. > > Let me see if I understand this. Assuming 4k pages, the region > described above spans *two* 2M entries: > > (a) ff00ab2000-ff00c00000, part of ff00a00000-ff00c00000 > (b) ff00c00000-ff00db2000, part of ff00c00000-ff00e00000 > > (a) has no valid mapping, but (b) does. Because we fail to correctly > align on a block boundary when skipping (a), we also skip (b), which > is then left mapped. > > Did I get it right? If so, yes, this is... annoying. > > Understanding the circumstances this triggers in would be most > interesting. This current code seems to assume that we get ranges > aligned to mapping boundaries, but I seem to remember that the old > code did use the stage2_*_addr_end() helpers to deal with this case. > > Will: I don't think things have changed in that respect, right? Indeed we should still use stage2_*_addr_end(), especially in the unmap path that is mentioned here, so it would be helpful to have a little bit more context. > > Without this fix, userspace "segment fault" error can be easily > > triggered by running simple gVisor runsc cases on an Ampere Altra > > server: > > docker run --runtime=runsc -it --rm ubuntu /bin/bash > > > > In container: > > for i in `seq 1 100`;do ls;done > > The workload on its own isn't that interesting. What I'd like to > understand is what happens on the host during that time. > > > > > Reported-by: Howard Zhang > > Signed-off-by: Jia He > > --- > > arch/arm64/kvm/hyp/pgtable.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > > index bdf8e55ed308..4d99d07c610c 100644 > > --- a/arch/arm64/kvm/hyp/pgtable.c > > +++ b/arch/arm64/kvm/hyp/pgtable.c > > @@ -225,6 +225,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data, > > goto out; > > > > if (!table) { > > + data->addr = ALIGN_DOWN(data->addr, kvm_granule_size(level)); > > data->addr += kvm_granule_size(level); > > goto out; > > } > > It otherwise looks good to me. Quentin, Will: unless you object to > this, I plan to take it in the next round of fixes with Though I'm still unsure how we hit that today, the change makes sense on its own I think, so no objection from me. Thanks, Quentin _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm 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=-13.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_ADSP_CUSTOM_MED,DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=unavailable 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 D2C5CC433E0 for ; Wed, 3 Mar 2021 19:09:42 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 1C6D660295 for ; 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[35.233.69.230]) by smtp.gmail.com with ESMTPSA id r10sm7196657wmh.45.2021.03.03.03.09.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Mar 2021 03:09:01 -0800 (PST) Date: Wed, 3 Mar 2021 11:08:56 +0000 From: Quentin Perret To: Marc Zyngier Cc: Jia He , kvmarm@lists.cs.columbia.edu, James Morse , Julien Thierry , Suzuki K Poulose , Catalin Marinas , Will Deacon , Gavin Shan , Yanan Wang , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: arm64: Fix unaligned addr case in mmu walking Message-ID: References: <20210303024225.2591-1-justin.he@arm.com> <87sg5czhny.wl-maz@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <87sg5czhny.wl-maz@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210303_111008_776695_46B0F7F6 X-CRM114-Status: GOOD ( 31.57 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wednesday 03 Mar 2021 at 09:54:25 (+0000), Marc Zyngier wrote: > Hi Jia, > > On Wed, 03 Mar 2021 02:42:25 +0000, > Jia He wrote: > > > > If the start addr is not aligned with the granule size of that level. > > loop step size should be adjusted to boundary instead of simple > > kvm_granual_size(level) increment. Otherwise, some mmu entries might miss > > the chance to be walked through. > > E.g. Assume the unmap range [data->addr, data->end] is > > [0xff00ab2000,0xff00cb2000] in level 2 walking and NOT block mapping. > > When does this occur? Upgrade from page mappings to block? Swap out? > > > And the 1st part of that pmd entry is [0xff00ab2000,0xff00c00000]. The > > pmd value is 0x83fbd2c1002 (not valid entry). In this case, data->addr > > should be adjusted to 0xff00c00000 instead of 0xff00cb2000. > > Let me see if I understand this. Assuming 4k pages, the region > described above spans *two* 2M entries: > > (a) ff00ab2000-ff00c00000, part of ff00a00000-ff00c00000 > (b) ff00c00000-ff00db2000, part of ff00c00000-ff00e00000 > > (a) has no valid mapping, but (b) does. Because we fail to correctly > align on a block boundary when skipping (a), we also skip (b), which > is then left mapped. > > Did I get it right? If so, yes, this is... annoying. > > Understanding the circumstances this triggers in would be most > interesting. This current code seems to assume that we get ranges > aligned to mapping boundaries, but I seem to remember that the old > code did use the stage2_*_addr_end() helpers to deal with this case. > > Will: I don't think things have changed in that respect, right? Indeed we should still use stage2_*_addr_end(), especially in the unmap path that is mentioned here, so it would be helpful to have a little bit more context. > > Without this fix, userspace "segment fault" error can be easily > > triggered by running simple gVisor runsc cases on an Ampere Altra > > server: > > docker run --runtime=runsc -it --rm ubuntu /bin/bash > > > > In container: > > for i in `seq 1 100`;do ls;done > > The workload on its own isn't that interesting. What I'd like to > understand is what happens on the host during that time. > > > > > Reported-by: Howard Zhang > > Signed-off-by: Jia He > > --- > > arch/arm64/kvm/hyp/pgtable.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > > index bdf8e55ed308..4d99d07c610c 100644 > > --- a/arch/arm64/kvm/hyp/pgtable.c > > +++ b/arch/arm64/kvm/hyp/pgtable.c > > @@ -225,6 +225,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data, > > goto out; > > > > if (!table) { > > + data->addr = ALIGN_DOWN(data->addr, kvm_granule_size(level)); > > data->addr += kvm_granule_size(level); > > goto out; > > } > > It otherwise looks good to me. Quentin, Will: unless you object to > this, I plan to take it in the next round of fixes with Though I'm still unsure how we hit that today, the change makes sense on its own I think, so no objection from me. Thanks, Quentin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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=-23.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 A148CC4332B for ; Wed, 3 Mar 2021 15:53:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 75C8364EE1 for ; Wed, 3 Mar 2021 15:53:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1452653AbhCCPwq (ORCPT ); Wed, 3 Mar 2021 10:52:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48126 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351168AbhCCLJo (ORCPT ); Wed, 3 Mar 2021 06:09:44 -0500 Received: from mail-wm1-x32f.google.com (mail-wm1-x32f.google.com [IPv6:2a00:1450:4864:20::32f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B0FD1C061788 for ; Wed, 3 Mar 2021 03:09:03 -0800 (PST) Received: by mail-wm1-x32f.google.com with SMTP id u125so5906529wmg.4 for ; Wed, 03 Mar 2021 03:09:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=MrgKs7AaAPjSu71bqqbhqpKHLtrghctRiTu/BX2ygw8=; b=FRekRJ5Nz3cuYK/fdGOcgaM6AWa1qil920H3kKq4lFukOc3ZwD8SjK6qpnsMwV2TQ7 5BnY2nCQ3Z0rXltTRr1gF64IuwVC5GZ/7BDGhOCKm3M4Zfdj7nCQ8GgtYDv/XreD1tMa nerPCo83Rz7nSde1dO/VwB6Gjx6qZ8P2QhRVi93aTOeVz/kTLEbuh4Z6rIhJOcYxiSm6 d4uZxTqyKSiQMrgs1l29hwka1QnS4gUVQQqJ0ZXg9MzeyCpQvCdsNBc1TqsZWvzwfe6V nSRA53tBAXvZdl1XZ/PMZ+HTLRuTbD/I/CgDQN+8XBRm5+hI9ma1/pc9+BbA7H3rgUSF Kk3g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=MrgKs7AaAPjSu71bqqbhqpKHLtrghctRiTu/BX2ygw8=; b=DwX9RfAqtsYPMy30G27IUUD4Cz/6vcBk+JR3I9gowySpQ/59nmP+n53+Jq1Nkeispl Yamim6bJhwmUn9wYqUFXfcgfj3zhfBC5g9enojBOVE2i2XOqgHyl3/eRfwmI+JPiFQCi OOXRCmtPYBSLxGNgtxWnv1ocrTxQh8FqaZrWgEs9/8B1cS6EF5WGToMz10W+1dl8t17R Sd49lM8x/z9YM1ZsnnLdbrGz8v8I8RwXHZqYvZ64w5ayYczli617LjcZT3Z4KnqwfM3s 9GOM8W8X30Mr2averhNs6L8bzrZCtXB0e97TOo52q3aDWPgPcUNIWeFg7z99TqVFRmH9 fwvw== X-Gm-Message-State: AOAM531p0HUSYXMZEviCaCvEU+/I4fFTILGuDawYZGdYTOZE5Zp6nG0U JtupELTnzfhcBFQ25jqg5iRdlA== X-Google-Smtp-Source: ABdhPJxFT/FTy1GsdpssFmrNcBfUaVBDWruZyYIsCWz48j1d9N4bImoC/8FkC4KeJ3Nuf3JpJ9Rp5A== X-Received: by 2002:a1c:bb89:: with SMTP id l131mr8855627wmf.47.1614769741728; Wed, 03 Mar 2021 03:09:01 -0800 (PST) Received: from google.com (230.69.233.35.bc.googleusercontent.com. [35.233.69.230]) by smtp.gmail.com with ESMTPSA id r10sm7196657wmh.45.2021.03.03.03.09.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Mar 2021 03:09:01 -0800 (PST) Date: Wed, 3 Mar 2021 11:08:56 +0000 From: Quentin Perret To: Marc Zyngier Cc: Jia He , kvmarm@lists.cs.columbia.edu, James Morse , Julien Thierry , Suzuki K Poulose , Catalin Marinas , Will Deacon , Gavin Shan , Yanan Wang , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: arm64: Fix unaligned addr case in mmu walking Message-ID: References: <20210303024225.2591-1-justin.he@arm.com> <87sg5czhny.wl-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87sg5czhny.wl-maz@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday 03 Mar 2021 at 09:54:25 (+0000), Marc Zyngier wrote: > Hi Jia, > > On Wed, 03 Mar 2021 02:42:25 +0000, > Jia He wrote: > > > > If the start addr is not aligned with the granule size of that level. > > loop step size should be adjusted to boundary instead of simple > > kvm_granual_size(level) increment. Otherwise, some mmu entries might miss > > the chance to be walked through. > > E.g. Assume the unmap range [data->addr, data->end] is > > [0xff00ab2000,0xff00cb2000] in level 2 walking and NOT block mapping. > > When does this occur? Upgrade from page mappings to block? Swap out? > > > And the 1st part of that pmd entry is [0xff00ab2000,0xff00c00000]. The > > pmd value is 0x83fbd2c1002 (not valid entry). In this case, data->addr > > should be adjusted to 0xff00c00000 instead of 0xff00cb2000. > > Let me see if I understand this. Assuming 4k pages, the region > described above spans *two* 2M entries: > > (a) ff00ab2000-ff00c00000, part of ff00a00000-ff00c00000 > (b) ff00c00000-ff00db2000, part of ff00c00000-ff00e00000 > > (a) has no valid mapping, but (b) does. Because we fail to correctly > align on a block boundary when skipping (a), we also skip (b), which > is then left mapped. > > Did I get it right? If so, yes, this is... annoying. > > Understanding the circumstances this triggers in would be most > interesting. This current code seems to assume that we get ranges > aligned to mapping boundaries, but I seem to remember that the old > code did use the stage2_*_addr_end() helpers to deal with this case. > > Will: I don't think things have changed in that respect, right? Indeed we should still use stage2_*_addr_end(), especially in the unmap path that is mentioned here, so it would be helpful to have a little bit more context. > > Without this fix, userspace "segment fault" error can be easily > > triggered by running simple gVisor runsc cases on an Ampere Altra > > server: > > docker run --runtime=runsc -it --rm ubuntu /bin/bash > > > > In container: > > for i in `seq 1 100`;do ls;done > > The workload on its own isn't that interesting. What I'd like to > understand is what happens on the host during that time. > > > > > Reported-by: Howard Zhang > > Signed-off-by: Jia He > > --- > > arch/arm64/kvm/hyp/pgtable.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > > index bdf8e55ed308..4d99d07c610c 100644 > > --- a/arch/arm64/kvm/hyp/pgtable.c > > +++ b/arch/arm64/kvm/hyp/pgtable.c > > @@ -225,6 +225,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data, > > goto out; > > > > if (!table) { > > + data->addr = ALIGN_DOWN(data->addr, kvm_granule_size(level)); > > data->addr += kvm_granule_size(level); > > goto out; > > } > > It otherwise looks good to me. Quentin, Will: unless you object to > this, I plan to take it in the next round of fixes with Though I'm still unsure how we hit that today, the change makes sense on its own I think, so no objection from me. Thanks, Quentin