Re: [PATCH v2 0/4] KVM: arm64: vcpu sysreg accessor rework

[Oliver Upton <oliver.upton@linux.dev>]

On Tue, Jun 03, 2025 at 08:08:20AM +0100, Marc Zyngier wrote:
> This series tries to bring some sanity to the way the RESx masks
> are applied when accessing the in-memory view of the guest's
> system registers.
> 
> Currently, we have *one* accessor (__vcpu_sys_reg()) that can either
> be used as a rvalue or lvalue while that applies the RESx masks behind
> the scenes. This works fine when used as a rvalue.
> 
> However, when used as a lvalue, it does the wrong thing, as it only
> sanitises the value we're about to overwrite. This is pointless work
> and potentially hides bugs.
> 
> I propose that we move to a set of store-specific accessors (for
> assignments and RMW) instead of the lvalue hack, ensuring that the
> assigned value is the one that gets sanitised. This then allows the 
> legacy accessor to be converted to rvalue-only.

Very happy with how this is shaping up.

> Given the level of churn this introduces, I'd like this to land very
> early in the cycle. Either before 6.16-rc2, or early in 6.17.

What's your mood on sneaking this in as a fix for 6.16? It'd fix the
unmasked write bug you mention and hopefully give a semi-stable / early
base for building the 6.17 content on top off.

Otherwise this will be the very first thing I take for 6.17.

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>

Thanks,
Oliver