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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 5E3D2C44501 for ; Mon, 13 Jul 2026 10:32:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc: To:From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=eTqU3dT6rzoa78gvVlfTAv7/fiNLfAlCGxoZbc0EA5A=; b=mAYaNa6tPf3VCbSaNM3P9kKFzX ywYPmEtgKa5XiZeIFlOwAc/ZG8qLQzdU2+h8eSegKhnoSpb0/kxGZIHBND9Lod+aOZBwfiZb/kYbM jloE9Md0vjsErTYDFfgA2lparFtWMme7S2gunMY6OIg+Zo7vPNGzTwiKeFMS7RlTFGyOzXDMQdRtz NiwIgA4Siuji2JHPXeoeH6E26tStOZZ8ZGsU4d/EZcm0ZwQIgcqLls3OsoezQMZA7gaeZ5jDiacZD 5PvtRzaHE1ncUIS8AgVwsq/4ZUdMktAjWbJVPnqN4WmvqFtGR33+r07FC/d6kaGIpmn9wMCthpl/O BJu2IumQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wjDx4-00000008tbY-08oF; Mon, 13 Jul 2026 10:31:54 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wjDx1-00000008tax-3KkK for linux-arm-kernel@lists.infradead.org; Mon, 13 Jul 2026 10:31:53 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B37A3152B; Mon, 13 Jul 2026 03:31:46 -0700 (PDT) Received: from LeoBrasDK.cambridge.arm.com (LeoBrasDK.cambridge.arm.com [10.2.212.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1EE503F93E; Mon, 13 Jul 2026 03:31:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1783938711; bh=2vc9t6B108vjh8OZgKdBi0NW18wPseEjqvmkpgNcas0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=caaVXN7+HkmYFEIkjnbg1V0D09tJ1taUdZpyFpfkeefbzWb5Qc7rvcHloS4iD39Bg itoLyzAmdV8gyNuviTOCt6ga7UL+xGxWnD2nG3eRypXbSrKLxYhGyFys8JVMJ5w/iY p25v5MH2urDLktoOIhgcqHi6aP078fNagADwpQFc= From: Leonardo Bras To: Tian Zheng Cc: Leonardo Bras , maz@kernel.org, oupton@kernel.org, catalin.marinas@arm.com, will@kernel.org, yuzenghui@huawei.com, wangzhou1@hisilicon.com, yangjinqian1@huawei.com, caijian11@h-partners.com, liuyonglong@huawei.com, yezhenyu2@huawei.com, yubihong@huawei.com, linuxarm@huawei.com, joey.gouly@arm.com, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, seiden@linux.ibm.com, suzuki.poulose@arm.com Subject: Re: [PATCH v4 0/6] Support the FEAT_HDBSS introduced in Armv9.5 Date: Mon, 13 Jul 2026 11:31:46 +0100 Message-ID: X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260709104026.2612599-1-zhengtian10@huawei.com> References: <20260709104026.2612599-1-zhengtian10@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260713_033151_914984_DDAE246F X-CRM114-Status: GOOD ( 30.90 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Jul 09, 2026 at 06:40:20PM +0800, Tian Zheng wrote: > This series of patches add support to the Hardware Dirty state tracking > Structure (HDBSS) feature, which is introduced by the ARM architecture > in the DDI0601 (ID121123) version. > > The HDBSS feature is an extension to the architecture that enhances > tracking translation table descriptors' dirty state, identified as > FEAT_HDBSS. This feature utilizes hardware assistance to achieve dirty > page tracking, aiming to significantly reduce the overhead of scanning > for dirty pages. > > The purpose of this feature is to make the execution overhead of live > migration lower to both the guest and the host, compared to existing > approaches (write-protect or search stage-2 tables). > > The required sysreg definitions for FEAT_HDBSS have been merged into > arm64 /sysregs: > [1/5] arm64/sysreg: Add HDBSS related register information > https://git.kernel.org/arm64/c/72f7be0c2e30 > > > After these patches, the kernel automatically enables HDBSS when dirty > logging is enabled on any memslot, and disables HDBSS when dirty logging > is disabled on all memslots. This series does not support dirty ring > mode. > > Depends-on: "KVM: arm64: Enable eager hugepage splitting if HDBSS is available" > https://lore.kernel.org/linux-arm-kernel/20260629111820.1873540-3-leo.bras@arm.com/ On this, FYI, there have been some discussion on this: https://lore.kernel.org/all/alETGFD2Ogx6N0HB@LeoBrasDK/ Oliver's suggestion is that we don't automatically enable eager splitting, but instead we have different behaviours if the user enables it. This is still under discussion there, but I think it can be useful reading. > > This dependency is mandatory. Unlike v3, where DBM was added lazily on > the first dirty access via a page fault, v4 injects DBM into pgt->flags > at stage-2 MMU initialization time. Combined with HDBSS being auto-enabled > during migration setup, the first dirty access no longer triggers a page > fault. Consequently, if lazy hugepage splitting were relied upon (which > requires a page fault to trigger splitting), hugepages would never be > split, leading to guest hang after migration. Leonardo's patch above > ensures eager hugepage splitting is enabled (chunk_size != 0) when HDBSS > is available, guaranteeing that hugepages are properly split before > migration starts. > > v3: https://lore.kernel.org/linux-arm-kernel/20260225040421.2683931-1-zhengtian10@huawei.com/ > > v3->v4 changes: > - Merge sysreg definitions into the FEAT_HDBSS detection patch (was a > separate patch in v3). > - Add auto DBM (Dirty Bit Modifier) support as a new patch, suggested > by Leonardo Bras. DBM is now controlled as a page-table level flag > (KVM_PGTABLE_S2_DBM) rather than per-PTE. Note that DBM is injected > at stage-2 MMU creation time, not lazily on first dirty access. This > means the first write to a dirty-logged page does not generate a > page fault, which is a key reason for the mandatory dependency on > Leonardo's eager hugepage splitting patch (see Depends-on above). > - Split the v3 "Enable HDBSS support and handle HDBSSF events" patch > into three patches: per-vCPU buffer management, fault handling and > buffer flush, and auto enable/disable on dirty logging change. This > implements kernel-managed automatic HDBSS enable/disable. > - Remove the KVM_CAP_ARM_HW_DIRTY_STATE_TRACK ioctl for manual HDBSS > on/off. HDBSS is now automatically enabled/disabled based on dirty > logging state via kvm_arch_commit_memory_region(). > - Change HDBSS buffer flush triggers to vcpu_put, check_vcpu_requests, > and kvm_handle_guest_abort. > - Store hdbss_order at VM level (kvm->arch.hdbss_order) instead of > per-vCPU, since all vCPUs share the same order. > - Document patch is not included in this version; will be sent in a > follow-up series. > > Leonardo Bras (1): > KVM: arm64: Enable eager hugepage splitting if HDBSS is available > > Tian Zheng (2): > KVM: arm64: Add support for FEAT_HDBSS > KVM: arm64: Add auto DBM support for hardware dirty tracking > > eillon (3): > KVM: arm64: Add HDBSS per-vCPU buffer management > KVM: arm64: Add HDBSS fault handling and buffer flush > KVM: arm64: Add auto HDBSS enable/disable on dirty logging change > > arch/arm64/include/asm/cpufeature.h | 5 + > arch/arm64/include/asm/esr.h | 5 + > arch/arm64/include/asm/kvm_dirty_bit.h | 29 ++++ > arch/arm64/include/asm/kvm_host.h | 14 ++ > arch/arm64/include/asm/kvm_pgtable.h | 4 + > arch/arm64/include/asm/sysreg.h | 11 ++ > arch/arm64/kernel/cpufeature.c | 12 ++ > arch/arm64/kvm/Makefile | 1 + > arch/arm64/kvm/arm.c | 29 ++++ > arch/arm64/kvm/dirty_bit.c | 219 +++++++++++++++++++++++++ > arch/arm64/kvm/hyp/pgtable.c | 35 +++- > arch/arm64/kvm/hyp/vhe/switch.c | 15 ++ > arch/arm64/kvm/mmu.c | 19 ++- > arch/arm64/kvm/reset.c | 4 + > arch/arm64/tools/cpucaps | 1 + > 15 files changed, 399 insertions(+), 4 deletions(-) > create mode 100644 arch/arm64/include/asm/kvm_dirty_bit.h > create mode 100644 arch/arm64/kvm/dirty_bit.c > > -- > 2.33.0 >