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 4D95D3093DD; Mon, 13 Jul 2026 16:27:19 +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=1783960042; cv=none; b=bCFiUqUP8FbnLbLk38wmJc+8CO8VSd7w04mmm2rGCgMegKE3tqxwvptASFb7VaNp7ZgtoF7DpBD3VUwT8f3KvG5GemGjalK5wfOEU+gCh09QLqERz3ld51zGEwSdoEms4g3XVx1LH0CV/F0JlGYMTi3igyTQm/BHXv4qHyJfPbs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783960042; c=relaxed/simple; bh=9/dA430eBn0wUibKGs9m2V3IKUxqPP4CnsyZ/vCU/qs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type:Content-Disposition; b=dv5sRsHNLsRULGsYpXbICB/ZAcHYFgd6quXcjl7bjQh3eMbJ+Ks7/aekucBhtaHUyxFyIRVy7DZGj/DgkJC0sJzeMS6+oqtKMRallHXbaYwthrlDhZheP+uTt2hjIA+tt9gis4QZnrQRyzRkv2HvXxPvPaeS1TWiy6JLtszY3/s= 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=rQArY0Lh; 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="rQArY0Lh" 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 481831576; Mon, 13 Jul 2026 09:27:14 -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 9F11D3F7B4; Mon, 13 Jul 2026 09:27:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1783960038; bh=9/dA430eBn0wUibKGs9m2V3IKUxqPP4CnsyZ/vCU/qs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rQArY0LhHeb5W5EWwG94eauzoEVyWqhOvcyOeLx/rgVIDDk4KOvti1M6f+btBGsce 9Aq68e0rcryOv5o8bxmt7e2c2/4tLhdeESV1+y3iEq1pUSBzfo/TlFlLDcKGnWuyd5 GmS527v7pbeRChy4Kt/+Q+CYJzF2OsnvKYeFJu6s= 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 17:27:09 +0100 Message-ID: X-Mailer: git-send-email 2.55.0 In-Reply-To: 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 Mon, Jul 13, 2026 at 11:31:46AM +0100, Leonardo Bras wrote: > 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 > > Also, please remember to include the base commit, so it can be applied for testing/reviewing.