linux-kernel - Re: [RFC PATCH 16/27] KVM: arm64: Prepare Hyp memory protection

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Date:   Tue, 8 Dec 2020 09:40:27 +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>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" 
        <kvmarm@...ts.cs.columbia.edu>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE" 
        <devicetree@...r.kernel.org>, kernel-team@...roid.com,
        android-kvm@...gle.com
Subject: Re: [RFC PATCH 16/27] KVM: arm64: Prepare Hyp memory protection

On Mon, Dec 07, 2020 at 02:11:20PM +0000, Quentin Perret wrote:
> On Monday 07 Dec 2020 at 13:40:52 (+0000), Will Deacon wrote:
> > Why not use the RESERVEDMEM_OF_DECLARE() interface for the hypervisor
> > memory? That way, the hypervisor memory can either be statically partitioned
> > as a carveout or allocated dynamically for us -- we wouldn't need to care.
> 
> Yup, I did consider that, but the actual amount of memory we need to
> reserve for the hypervisor depends on things such as the size of struct
> hyp_page, which depends on the kernel you're running (that is, it might
> change over time). So, that really felt like something the kernel should
> be doing, to keep the DT backward compatible, ... Or did you have
> something more elaborate in mind?

No, that's fair. Just wanted to make sure we had a good reason not to use
the existing memory reservation code.

Will