Re: [RFC PATCH v2 0/2] KVM: arm64: Add support for BBM level 3

[Linu Cherian]

Hi,

On Thu, Jul 23, 2026 at 06:21:38PM +0000, Mostafa Saleh wrote:
> This patch series adds support for BBM level 3 to KVM pgtable, it
> depends on [1]
> 
> Changes from v1:
> https://lore.kernel.org/all/20260717130901.2239134-1-smostafa@xxxxxxxxxx/
> - Limit BBML3 to systems with FWB and DIC and remove race check.
> 
> Motivation
> ==========
> I have been looking into this for the context of:
> - Page table sharing between the host CPU stage-2 and the SMMUv3 for
>   protected KVM.
> - Use the pagtable code to populate SMMUv3 stage-2 shadowed
>   page table [2]
> 
> However, BBM level 3 is still useful for CPU only operations as it
> avoids intermediately breaking translation.
> 
> Design
> ======
> Some of the conditions that BBM level 3 will be useful in (RWHZWS):
> 1) A change to a PTE memory type, shareability, cacheability or OA

Could you please clarify how BBM level 3 is helping this particular scenario ?
This is supposed to be a case where break before make is required.

Thanks,
Linu Cherian.