Re: [PATCH] KVM: arm64: Fix nVHE stacktrace VA bits mask

[Marc Zyngier <maz@kernel.org>]

Vincent,

Please add all the KVM/arm64 reviewers in the future (I added them
this time).

On Mon, 06 Jan 2025 18:32:13 +0000,
Vincent Donnefort <vdonnefort@google.com> wrote:
> 
> The hypervisor VA space size depends on both the ID map's
> (IDMAP_VA_BITS) and the kernel stage-1 (VA_BITS). When VA_BITS is
> smaller than IDMAP_VA_BITS (i.e. 39-bit), the stacktrace can contain
> addresses bigger than the current VA_BITS mask.
> 
> As the hyp_va_bits value needs to be used outside of the init code now,
> use a global variable, shared by all the kvm users in mmu.c, arm.c and
> now stacktrace.c.

I tend to dislike this approach for at least three reasons:

- it makes it hard to follow *when* hyp_va_bits is made valid, while
  passing the value as a parameter is self explanatory. Specially
  given how convoluted the nVHE/pKVM init is these days.

- it prevents the eventual use of *multiple* VA bit values (one for
  TTBR0, one for TTBR1) once the grand plan for hVHE is completed
  (right after full NV support is merged! ;-)

- it makes the change larger than it should be, specially for
  something that should be backported.

So I'd rather you keep the general shape of the code as it, and simply
publish this 'hyp_va_bits' for the purpose of the backtrace code.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.