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=-4.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, SPF_HELO_NONE 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 7A10FC47080 for ; Tue, 1 Jun 2021 12:02:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4C75E613AE for ; Tue, 1 Jun 2021 12:02:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233657AbhFAMDz (ORCPT ); Tue, 1 Jun 2021 08:03:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:33318 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230308AbhFAMDp (ORCPT ); Tue, 1 Jun 2021 08:03:45 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4C42F60200; Tue, 1 Jun 2021 12:02:04 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1lo35t-004oFR-Vk; Tue, 01 Jun 2021 13:02:02 +0100 Date: Tue, 01 Jun 2021 13:02:00 +0100 Message-ID: <87sg2123pj.wl-maz@kernel.org> From: Marc Zyngier To: Quentin Perret Cc: will@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com, catalin.marinas@arm.com, suzuki.poulose@arm.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kernel-team@android.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/7] KVM: arm64: Move hyp_pool locking out of refcount helpers In-Reply-To: <20210527125134.2116404-2-qperret@google.com> References: <20210527125134.2116404-1-qperret@google.com> <20210527125134.2116404-2-qperret@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: qperret@google.com, will@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com, catalin.marinas@arm.com, suzuki.poulose@arm.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kernel-team@android.com, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 27 May 2021 13:51:28 +0100, Quentin Perret wrote: > > The hyp_page refcount helpers currently rely on the hyp_pool lock for > serialization. However, this means the refcounts can't be changed from > the buddy allocator core as it already holds the lock, which means pages > have to go through odd transient states. > > For example, when a page is freed, its refcount is set to 0, and the > lock is transiently released before the page can be attached to a free > list in the buddy tree. This is currently harmless as the allocator > checks the list node of each page to see if it is available for > allocation or not, but it means the page refcount can't be trusted to > represent the state of the page even if the pool lock is held. > > In order to fix this, remove the pool locking from the refcount helpers, > and move all the logic to the buddy allocator. This will simplify the > removal of the list node from struct hyp_page in a later patch. Is there any chance some documentation could be added so that we have a record of what the locking boundaries are? Something along the line of what we have in arch/arm64/kvm/vgic/vgic.c, for example. Thanks, M. -- Without deviation from the norm, progress is not possible. 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=-4.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, SPF_HELO_NONE 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 55123C4708F for ; Tue, 1 Jun 2021 12:02:15 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id B2556613AE for ; Tue, 1 Jun 2021 12:02:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B2556613AE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 1EE3C4064F; Tue, 1 Jun 2021 08:02:14 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id aoYOOw5wcT9o; Tue, 1 Jun 2021 08:02:08 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 8712C407A0; Tue, 1 Jun 2021 08:02:08 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id AEE4640825 for ; Tue, 1 Jun 2021 08:02:06 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 0e0OoUhHQb+F for ; Tue, 1 Jun 2021 08:02:05 -0400 (EDT) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id A00C44064F for ; Tue, 1 Jun 2021 08:02:05 -0400 (EDT) Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4C42F60200; Tue, 1 Jun 2021 12:02:04 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1lo35t-004oFR-Vk; Tue, 01 Jun 2021 13:02:02 +0100 Date: Tue, 01 Jun 2021 13:02:00 +0100 Message-ID: <87sg2123pj.wl-maz@kernel.org> From: Marc Zyngier To: Quentin Perret Subject: Re: [PATCH 1/7] KVM: arm64: Move hyp_pool locking out of refcount helpers In-Reply-To: <20210527125134.2116404-2-qperret@google.com> References: <20210527125134.2116404-1-qperret@google.com> <20210527125134.2116404-2-qperret@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: qperret@google.com, will@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com, catalin.marinas@arm.com, suzuki.poulose@arm.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kernel-team@android.com, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: kernel-team@android.com, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, will@kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org 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 Thu, 27 May 2021 13:51:28 +0100, Quentin Perret wrote: > > The hyp_page refcount helpers currently rely on the hyp_pool lock for > serialization. However, this means the refcounts can't be changed from > the buddy allocator core as it already holds the lock, which means pages > have to go through odd transient states. > > For example, when a page is freed, its refcount is set to 0, and the > lock is transiently released before the page can be attached to a free > list in the buddy tree. This is currently harmless as the allocator > checks the list node of each page to see if it is available for > allocation or not, but it means the page refcount can't be trusted to > represent the state of the page even if the pool lock is held. > > In order to fix this, remove the pool locking from the refcount helpers, > and move all the logic to the buddy allocator. This will simplify the > removal of the list node from struct hyp_page in a later patch. Is there any chance some documentation could be added so that we have a record of what the locking boundaries are? Something along the line of what we have in arch/arm64/kvm/vgic/vgic.c, for example. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ 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=-4.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 AB007C47080 for ; Tue, 1 Jun 2021 12:12:00 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 6AC38610A1 for ; Tue, 1 Jun 2021 12:12:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6AC38610A1 Authentication-Results: mail.kernel.org; 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Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lo3EE-00GS2R-48; Tue, 01 Jun 2021 12:10:38 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1lo35w-00GHtj-Rc for linux-arm-kernel@lists.infradead.org; Tue, 01 Jun 2021 12:02:06 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4C42F60200; Tue, 1 Jun 2021 12:02:04 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1lo35t-004oFR-Vk; Tue, 01 Jun 2021 13:02:02 +0100 Date: Tue, 01 Jun 2021 13:02:00 +0100 Message-ID: <87sg2123pj.wl-maz@kernel.org> From: Marc Zyngier To: Quentin Perret Cc: will@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com, catalin.marinas@arm.com, suzuki.poulose@arm.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kernel-team@android.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/7] KVM: arm64: Move hyp_pool locking out of refcount helpers In-Reply-To: <20210527125134.2116404-2-qperret@google.com> References: <20210527125134.2116404-1-qperret@google.com> <20210527125134.2116404-2-qperret@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: qperret@google.com, will@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com, catalin.marinas@arm.com, suzuki.poulose@arm.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kernel-team@android.com, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210601_050204_993746_7F64BF20 X-CRM114-Status: GOOD ( 23.94 ) 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 Thu, 27 May 2021 13:51:28 +0100, Quentin Perret wrote: > > The hyp_page refcount helpers currently rely on the hyp_pool lock for > serialization. However, this means the refcounts can't be changed from > the buddy allocator core as it already holds the lock, which means pages > have to go through odd transient states. > > For example, when a page is freed, its refcount is set to 0, and the > lock is transiently released before the page can be attached to a free > list in the buddy tree. This is currently harmless as the allocator > checks the list node of each page to see if it is available for > allocation or not, but it means the page refcount can't be trusted to > represent the state of the page even if the pool lock is held. > > In order to fix this, remove the pool locking from the refcount helpers, > and move all the logic to the buddy allocator. This will simplify the > removal of the list node from struct hyp_page in a later patch. Is there any chance some documentation could be added so that we have a record of what the locking boundaries are? Something along the line of what we have in arch/arm64/kvm/vgic/vgic.c, for example. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel