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From: Oliver Upton <oliver.upton@linux.dev>
To: Marc Zyngier <maz@kernel.org>
Cc: kvmarm@lists.linux.dev, kvm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Volodymyr Babchuk <volodymyr_babchuk@epam.com>,
	Joey Gouly <joey.gouly@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>
Subject: Re: [PATCH 2/2] KVM: arm64: Fix vcpu_{read,write}_sys_reg() accessors
Message-ID: <aJ-C1-t34aVmHLjY@linux.dev>
References: <20250809144811.2314038-1-maz@kernel.org>
 <20250809144811.2314038-3-maz@kernel.org>
 <aJuixWlc87f2UlK0@linux.dev>
 <86ikipev46.wl-maz@kernel.org>
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On Thu, Aug 14, 2025 at 05:16:57PM +0100, Marc Zyngier wrote:
> My current conclusion is that a macro hack is not really practical, if
> only because we end-up here from out-of-line C code, and that at this
> stage we've lost all symbolic information.
> 
> We *could* take the nuclear option of re-modelling the sysreg enum as
> a bunch of #define, similar to the way we deal with vcpu flags, and
> have accessors for the various bits of information, but that comes
> with two different problems:
> 
> - we don't have a good way to iterate over symbolic registers
> 
> - we need to repaint a large portion of the code base
> 
> Given that, I've taken another approach, which is to move all these
> things close together (no more inlining), and add enough WARN_ON()s
> that you really have to try and game the code to miss something and
> not get caught. In the process, I found a couple of extra stragglers
> that are always loaded when running a 32bit guest (the *32_EL2
> registers...).
> 
> I've pushed the current state on my kvm-arm64/at-fixes-6.17 branch,
> and I'll try to repost patches over the weekend.

Thanks! I've taken a glance at the branch and LGTM. Just wanted to make
sure we have sufficient idiotproofing for the next time I misuse this
stuff ;-)

Best,
Oliver