Re: [PATCH v4 00/10] Independent per-CPU data section for nVHE

[Christopher Lameter]

On Tue, 22 Sep 2020, David Brazdil wrote:

> Introduce '.hyp.data..percpu' as part of ongoing effort to make nVHE
> hyp code self-contained and independent of the rest of the kernel.

The percpu subsystems point is to enable the use of special hardware
instructions that can perform address calculation and a memory operation
in one interruptible instruction. This is in particular useful to avoid
higher overhead for memory management related counters because preempt
disable/enable etc can be avoided.

ARM cannot do that and thus has a LC/SC loop.

This is a patchset for ARM64 so its not clear to me what kind of advantage
there would be against a simple implementation that does a regular fetch
from a base address with an offset.

> Main benefits:
>  * independent nVHE per-CPU data section that can be unmapped from host,
>  * more robust linking of nVHE hyp code,
>  * no need for hyp-specific macros to access per-CPU variables.

Maybe simply don't use percpu variables for your arm code? Those pointers
to data will be much more indepedent of the rest of the kernel and allow a
much higher degree of being self-contained.