linux-kernel - Re: [PATCH v3 10/15] KVM: arm64: Introduce wrappers for host and hyp spin lock accessors

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Message-ID: <20211214145222.GC14837@willie-the-truck>
Date:   Tue, 14 Dec 2021 14:52:23 +0000
From:   Will Deacon <will@...nel.org>
To:     Andrew Walbran <qwandor@...gle.com>
Cc:     Quentin Perret <qperret@...gle.com>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v3 10/15] KVM: arm64: Introduce wrappers for host and hyp
 spin lock accessors

On Tue, Dec 14, 2021 at 02:48:30PM +0000, Andrew Walbran wrote:
> On Wed, 1 Dec 2021 at 17:04, 'Quentin Perret' via kernel-team
> <kernel-team@...roid.com> wrote:
> >
> > From: Will Deacon <will@...nel.org>
> >
> > In preparation for adding additional locked sections for manipulating
> > page-tables at EL2, introduce some simple wrappers around the host and
> > hypervisor locks so that it's a bit easier to read and bit more difficult
> > to take the wrong lock (or even take them in the wrong order).
> Looks good, but how does this help prevent taking locks in the wrong order?

I just found that I would easily forget what exactly was protected by
"pkvm_pgd_lock" and so relating that back to "take host before hyp" was
error-prone. Having helpers with "host" and "hyp" in the name helps me with
that, at least.

Will