Re: [PATCH v3 05/15] arm64: kvm: Build hyp-entry.S separately for VHE/nVHE

From: David Brazdil <dbrazdil@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: kernel-team@android.com, android-kvm@google.com,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v3 05/15] arm64: kvm: Build hyp-entry.S separately for VHE/nVHE
Date: Mon, 22 Jun 2020 11:20:41 +0100	[thread overview]
Message-ID: <20200622102041.myve2otyoj5q7j5s@google.com> (raw)
In-Reply-To: <5029f8fb4a7816e11de7469c09347c79@kernel.org>

Hi Marc,

> > -	void *dst = lm_alias(__bp_harden_hyp_vecs + slot * SZ_2K);
> > +	char *vec = has_vhe() ? __bp_harden_hyp_vecs
> > +			      : kvm_nvhe_sym(__bp_harden_hyp_vecs);
> 
> If we get this construct often, then something that abstracts
> the uggliness of the symbol duality would be nice...

Agreed, I do hope that this will end up being limited to finding the address of
the hyp-init vector once EL2 becomes self-contained. Even this vector selection
can be done in EL2 where the symbol duality does not exist.
If we were to hide it, there is a trade off between code "elegance" and clarity
of what's happening under the hood. I was thinking we could extract this
`has_vhe() ? foo : __kvm_nvhe_foo` as a `#define foo` but I do worry that
anybody debugging this code would be cursing my name. It would also not work
with other macros that take symbol names, notably kvm_ksym_ref. But that can be
rewritten to accept a pointer instead. The more verbose but less magic approach
is to have a bunch of different helpers for various situations, eg.
__pa_symbol_nvhe. What would be your preference?

-David
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm