Re: [PATCH 13/22] KVM: arm64: Set dirty state at stage-1

[Oliver Upton <oupton@kernel.org>]

On Fri, Jun 26, 2026 at 04:49:36PM +0100, Leonardo Bras wrote:
> On Tue, Jun 23, 2026 at 11:41:52AM -0700, Oliver Upton wrote:
> > Mark the descriptor as dirty if the permissions are sufficient to grant
> > write access. Note that compute_s1_direct_permissions() already
> > considers the DBM bit as writable.
> 
> IIUC the idea here is to avoid having a write fault when we first write to 
> that page. Is that correct?
> 
> When we have HAFDBS the fault does not happen, and it gets marked from 
> writeable-clean -> writeable-dirty by HAFDBS mechanism, which is cheap as 
> it happens to be a write to the pgtable when memory is first written to.
> 
> On the other hand, when we clean the dirty-bits for the first time, we 
> have to issue a write for every page that have been dirtied, in sequence.
> 
> An alternative would be not marking every page as dirty at first, in 
> exchange of possibly having a faster first clean pass.
> What do you think about it?

As Marc mentioned on the cover letter, this is unrelated to host dirty
tracking. I'm implementing HAFDBS as part of our pseudo-TLB refill for
nested. We need to mark translations as dirty in the nested S2 before
filling the shadow S2 with something that allows writes.

Thanks,
Oliver