[PATCH 0/5] arm64: Get rid of CnP

[Vladimir Murzin]

Hi Marc,

On 6/1/23 15:24, Marc Zyngier wrote:
> FEAT_TTCNP (née ARMv8.2-TTCNP, "Translation table Common not private
> translations", commonly known as CnP) was an attempt at allowing the
> sharing of TLBs in a SMT implementation. This was an interesting idea,
> but it never really went anywhere:
> 
> - There is only one implementation from ARM (Cortex-A65) that could
>   (conditional) be capable of using it, but this thing has never been
>   seen in the wild (shout if you have one!)
> 
> - There is one implementation from NVIDIA (Carmel) that has a
>   messed-up TLB invalidation "feature" that prevents the use of CnP
> 
> - The only other SMT implementation (Cavium-TX2) predates CnP, so it
>   doesn't implement it
> 
> - All the modern CPUs (which are not SMT) advertise CnP (it is
>   mandatory from ARMv8.2), but of course don't implement anything
>

I was told that it will benefit performance on LITTLE cores, like 
Cortex-A510 and Cortex-A520, which have a shared TLB, so it is not
quite SMT specific.

Cheers
Vladimir