linux-kernel - Re: [PATCH v2] KVM: arm64: Don't acquire RCU read lock for exclusive table walks

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Message-ID: <Y3Sb20U9rCIuOU3L@google.com>
Date:   Wed, 16 Nov 2022 08:14:19 +0000
From:   Oliver Upton <oliver.upton@...ux.dev>
To:     Marc Zyngier <maz@...nel.org>
Cc:     kvm@...r.kernel.org, Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-kernel@...r.kernel.org, kvmarm@...ts.linux.dev,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH v2] KVM: arm64: Don't acquire RCU read lock for exclusive
 table walks

On Wed, Nov 16, 2022 at 07:27:27AM +0000, Oliver Upton wrote:
> On Wed, Nov 16, 2022 at 03:08:49AM +0000, Marc Zyngier wrote:
> > I'm not crazy about this sort of parameters. I think it would make a
> > lot more sense to pass a pointer to the walker structure and do the
> > flag check inside the helper.
> > 
> > That way, we avoid extra churn if/when we need extra state or
> > bookkeeping around the walk.
> 
> Sure, let's go that way instead. v3 on the way lol :)

Well, going this route is going to require hoisting around a few things.

I'd very much prefer to keep the RCU indirection ifdeffery all in one
place, but I'll need to haul it all after the definitions of kvm_pgtable_walker
and kvm_pgtable_walk_flags but before the definition of kvm_pgtable
(as it needs kvm_pteref_t).

I'm not too bothered by it, but not quite as small of a bandaid this
time around.

--
Thanks,
Oliver