linux-kernel - Re: [RFC PATCH 15/27] of/fdt: Introduce early_init_dt_add_memory

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Message-ID: <20201118092547.GA2031536@google.com>
Date:   Wed, 18 Nov 2020 09:25:47 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        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>,
        Android Kernel Team <kernel-team@...roid.com>,
        android-kvm@...gle.com
Subject: Re: [RFC PATCH 15/27] of/fdt: Introduce
 early_init_dt_add_memory_hyp()

Hi Rob,

On Tuesday 17 Nov 2020 at 13:44:53 (-0600), Rob Herring wrote:
> Can this be done right after we add all the memblocks using the
> memblock API?

Possibly, but the thing I'm a bit worried about is the way 'no-map'
regions are removed from memblocks early on.

The EL2 object needs to know about these parts of memory too (and in
fact we may be able to enforce the 'no-map' attribute at the host stage
2 level as well). It's also possible we'll need to have portions of the
guests payload preloaded (and verified) by the bootloader into reserved
memory regions, possibly no-map, to make sure the host does not mess
with them in a normal use-case. So, I couldn't find a much better place
than this one but suggestions are very much welcome.

I'll have a go at the memblock stuff to see if I find a way to make it
work from that angle.

> I thought EFI would also need to be handled, but looks
> like it just calls early_init_dt_add_memory_arch(). That's odd
> especially for ACPI systems...
> 
> I don't really like putting what looks like an arm64 only hook here,
> but then I don't want an arm64 version of
> early_init_dt_add_memory_arch() either. We're almost to the point of
> getting rid of the arch specific ones. But I don't have a better
> suggestion currently.

Ack, the ugly truth is that this is likely to remain arm64-specific. I
figured this was simple enough that we might want to consider it,
though.

Thanks,
Quentin