linux-kernel - Re: [RFC PATCH v2 12/26] KVM: arm64: Introduce a Hyp buddy page allocator

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Message-ID: <20210204182404.GB21526@willie-the-truck>
Date:   Thu, 4 Feb 2021 18:24:05 +0000
From:   Will Deacon <will@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, android-kvm@...gle.com,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        Fuad Tabba <tabba@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        David Brazdil <dbrazdil@...gle.com>
Subject: Re: [RFC PATCH v2 12/26] KVM: arm64: Introduce a Hyp buddy page
 allocator

On Thu, Feb 04, 2021 at 06:19:36PM +0000, Quentin Perret wrote:
> On Thursday 04 Feb 2021 at 14:31:08 (+0000), Will Deacon wrote:
> > Just feels a bit backwards having __find_buddy() take an order parameter,
> > yet then return a page of the wrong order! __hyp_extract_page() always
> > passes the p->order as the order,
> 
> Gotcha, so maybe this is just a naming problem. __find_buddy() is simply
> a helper to lookup/index the vmemmap, but it's perfectly possible that
> the 'destination' page that is being indexed has already been allocated,
> and split up multiple time (and so at a different order), etc ... And
> that is the caller's job to decide.
> 
> How about __lookup_potential_buddy() ? Any suggestion?

Hey, my job here is to waffle incoherently and hope that you find bugs in
your own code. Now you want me to _name_ something! Jeez...

Ok, how about __find_buddy() does what it does today but doesn't take an
order argument, whereas __find_buddy_of_order() takes the order argument
and checks the page order before returning?

Will