Re: [PATCH 0/8] *** RFC: ARM KVM dirty tracking device ***

Janpoladyan, Lilit
2024-09-20T10:12:56Z

Hi Oliver,

﻿On 19.09.24, 11:12, "Oliver Upton" <oliver.upton@linux.dev <mailto:oliver.upton@linux.dev>> wrote:

> Hi Lilit,

> +cc kvmarm mailing list, get_maintainer is your friend :)

> On Wed, Sep 18, 2024 at 03:27:59PM +0000, Lilit Janpoladyan wrote:
> > An example of a device that tracks accesses to stage-2 translations and will
> > implement page_tracking_device interface is AWS Graviton Page Tracking Agent
> > (PTA). We'll be posting code for the Graviton PTA device driver in a separate
> > series of patches.

> In order to actually review these patches, we need to see an
> implementation of such a page tracking device. Otherwise it's hard to
> tell that the interface accomplishes the right abstractions.

We'll be posting driver patches in the coming weeks, they should explain device
functionality.

> Beyond that, I have some reservations about maintaining support for
> features that cannot actually be tested outside of your own environment.

I understand, we'll see how we can emulate the functionality and make interface
testable.

> > When ARM architectural solution (FEAT_HDBSS feature) is available, we intend to
> > use it via the same interface most likely with adaptations.

> Will the PTA stuff eventually get retired once you get support for FEAT_HDBSS
> in hardware?

We'd need to keep the interface for as long as hardware without FEAT_HDBSS
but with PTA is in use, hence the attempt of generalisation.

> I think the best way forward here is to implement the architecture, and
> hopefully after that your legacy driver can be made to fit the
> interface. The FVP implements FEAT_HDBSS, so there's some (slow)
> reference hardware to test against.

Thanks for the idea, we'll test with FVP, but we'd need FEAT_HDBSS
documentation for that. I don't think it's available yet, is it?

> This is a very interesting feature, so hopefully we can move towards
> something workable.

> --
> Thanks,
> Oliver

Thanks for the feedback, we'll be working on the discussed points,
Lilit

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