From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id F375D36604B; Mon, 13 Jul 2026 10:31:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783938714; cv=none; b=P5OQNy8+fUcwJYAC1RuRdqfWVTJ/3L8rkJc0cgaIJ7rSmM5i9pzDxFSixJvPP4Jnts8S+hhuabbn8R1RHxDDXmZvhdE8xlFyJzmnH01u3Zstlke4MMsYFirp7dp4e9jG/PE2d+sLFsratrRaAQRU487+9lzvSEdi4EF9SnXms7I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783938714; c=relaxed/simple; bh=2vc9t6B108vjh8OZgKdBi0NW18wPseEjqvmkpgNcas0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type:Content-Disposition; b=a7BDSwhKJA45/c2STy4DVNWozxNE8MLVai7u+FhJa5l8fpKYVTlbg1xFwYjA923c3TemnV/woNi1cyrV3enNpSsk+vXzZ1ul19DbZxK6WkwBO8LNqQzCjDgwBcPQW7mphOaU0h6Egf2qsZGYyGAz3VYiXMAjFZZEL7vstSx+AGU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=caaVXN7+; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="caaVXN7+" 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> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8bit 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 >