Re: [PATCH v3 0/5] Support the FEAT_HDBSS introduced in Armv9.5

[Tian Zheng <zhengtian10@huawei.com>]

On 3/31/2026 10:13 PM, Leonardo Bras wrote:
> On Wed, Feb 25, 2026 at 12:04:16PM +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).
>>
>> After these patches, users(such as qemu) can use the
>> KVM_CAP_ARM_HW_DIRTY_STATE_TRACK ioctl to enable or disable the HDBSS
>> feature before and after the live migration.
>>
>> v2:
>> https://lore.kernel.org/linux-arm-kernel/20251121092342.3393318-1-zhengtian10@huawei.com/
>>
>> v2->v3 changes:
>> - Remove the ARM64_HDBSS configuration option and ensure this feature
>> is only enabled in VHE mode.
>> - Move HDBSS-related variables to the arch-independent portion of the
>> kvm structure.
>> - Remove error messages during HDBSS enable/disable operations
>> - Change HDBSS buffer flushing from handle_exit to vcpu_put,
>> check_vcpu_requests, and kvm_handle_guest_abort.
>> - Add fault handling for HDBSS including buffer full, external abort,
>> and general protection fault (GPF).
>> - Add support for a 4KB HDBSS buffer size, mapped to the value 0b0000.
>> - Add a second argument to the ioctl to turn HDBSS on or off.
>>
>> Tian Zheng (1):
>>    KVM: arm64: Document HDBSS ioctl
>>
>> eillon (4):
>>    arm64/sysreg: Add HDBSS related register information
>>    KVM: arm64: Add support to set the DBM attr during memory abort
>>    KVM: arm64: Add support for FEAT_HDBSS
>>    KVM: arm64: Enable HDBSS support and handle HDBSSF events
>>
>>   Documentation/virt/kvm/api.rst       |  16 +++++
>>   arch/arm64/include/asm/cpufeature.h  |   5 ++
>>   arch/arm64/include/asm/esr.h         |   7 ++
>>   arch/arm64/include/asm/kvm_host.h    |  17 +++++
>>   arch/arm64/include/asm/kvm_mmu.h     |   1 +
>>   arch/arm64/include/asm/kvm_pgtable.h |   4 ++
>>   arch/arm64/include/asm/sysreg.h      |  11 +++
>>   arch/arm64/kernel/cpufeature.c       |  12 ++++
>>   arch/arm64/kvm/arm.c                 | 102 +++++++++++++++++++++++++++
>>   arch/arm64/kvm/hyp/pgtable.c         |   6 ++
>>   arch/arm64/kvm/hyp/vhe/switch.c      |  19 +++++
>>   arch/arm64/kvm/mmu.c                 |  70 ++++++++++++++++++
>>   arch/arm64/kvm/reset.c               |   3 +
>>   arch/arm64/tools/cpucaps             |   1 +
>>   arch/arm64/tools/sysreg              |  29 ++++++++
>>   include/uapi/linux/kvm.h             |   1 +
>>   tools/include/uapi/linux/kvm.h       |   1 +
>>   17 files changed, 305 insertions(+)
>>
>> --
>> 2.33.0
>>
>
> Hi Tian,
>
> I was thinking: maybe instead of putting the HDBSS (and HACDBS) stuff
> across a bunch of KVM files, we should try to focus them all on a single
> arch/arm64/kvm/dirty_bit.c file (plus a header such as
> arch/arm64/include/asm/kvm_dirty_bit.h).
>
> What is your opinion on that?
>
> Thanks!
> Leo


Sorry for the late reply. Yes, I had the same thought before. In the 
next version, I will

move all the HDBSS-related content into the same file, such as 
arch/arm64/kvm/dirty_bit.c

and arch/arm64/include/asm/kvm_dirty_bit.h.


Tian


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