Subject: Re: [PATCH v2 0/5] Support the FEAT_HDBSS introduced in Armv9.5

From: Marc Zyngier <[email-masked]>
Date: Fri, 21 Nov 2025 09:54:41 +0000

On Fri, 21 Nov 2025 09:23:37 +0000,
Tian Zheng <[email-masked]> 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. The goal of this feature is to reduce the cost of surveying
> for dirtied granules, with minimal effect on recording when a granule
> has been dirtied.
> 
> 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.
> 
> This feature is similar to Intel's Page Modification Logging (PML),
> offering hardware-assisted dirty tracking to reduce live migration
> overhead. With PML support expanding beyond Intel, HDBSS introduces a
> comparable mechanism for ARM.

Where is the change log describing what was changed compared to the
previous version?

We gave you extensive comments back in March. You never replied to the
feedback. And you now dump a whole set of patches, 6 months later,
without the slightest indication of what has changed?

Why should we make the effort to review this again?

	M.

-- 
Without deviation from the norm, progress is not possible.