Re: [RFC PATCH v2 15/26] of/fdt: Introduce early_init_dt_add_memory_hyp()

From: Rob Herring <robh+dt@kernel.org>
To: Quentin Perret <qperret@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Frank Rowand <frowand.list@gmail.com>,
	devicetree@vger.kernel.org, android-kvm@google.com,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Android Kernel Team <kernel-team@android.com>,
	"open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" 
	<kvmarm@lists.cs.columbia.edu>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	Fuad Tabba <tabba@google.com>,
	Mark Rutland <mark.rutland@arm.com>,
	David Brazdil <dbrazdil@google.com>
Subject: Re: [RFC PATCH v2 15/26] of/fdt: Introduce early_init_dt_add_memory_hyp()
Date: Tue, 12 Jan 2021 09:53:36 -0600	[thread overview]
Message-ID: <CAL_Jsq+o+t4YYXEW_nYqMsT4ubYJWe6Kdhu614RtrCqsHBtfLw@mail.gmail.com> (raw)
In-Reply-To: <X/2xlxx9Ucp4UZvL@google.com>

On Tue, Jan 12, 2021 at 8:26 AM Quentin Perret <qperret@google.com> wrote:
>
> On Tuesday 12 Jan 2021 at 08:10:47 (-0600), Rob Herring wrote:
> > On Tue, Jan 12, 2021 at 3:51 AM Quentin Perret <qperret@google.com> wrote:
> > >
> > > On Monday 11 Jan 2021 at 08:45:10 (-0600), Rob Herring wrote:
> > > > On Fri, Jan 8, 2021 at 6:16 AM Quentin Perret <qperret@google.com> wrote:
> > > > >
> > > > > Introduce early_init_dt_add_memory_hyp() to allow KVM to conserve a copy
> > > > > of the memory regions parsed from DT. This will be needed in the context
> > > > > of the protected nVHE feature of KVM/arm64 where the code running at EL2
> > > > > will be cleanly separated from the host kernel during boot, and will
> > > > > need its own representation of memory.
> > > >
> > > > What happened to doing this with memblock?
> > >
> > > I gave it a go, but as mentioned in v1, I ran into issues for nomap
> > > regions. I want the hypervisor to know about these memory regions (it's
> > > possible some of those will be given to protected guests for instance)
> > > but these seem to be entirely removed from the memblocks when using DT:
> > >
> > > https://elixir.bootlin.com/linux/latest/source/drivers/of/fdt.c#L1153
> > >
> > > EFI appears to do things differently, though, as it 'just' uses
> > > memblock_mark_nomap() instead of actively removing the memblock. And that
> > > means I could actually use the memblock API for EFI, but I'd rather
> > > have a common solution. I tried to understand why things are done
> > > differently but couldn't find an answer and kept things simple and
> > > working for now.
> > >
> > > Is there a good reason for not using memblock_mark_nomap() with DT? If
> > > not, I'm happy to try that.
> >
> > There were 2 patches to do that, but it never got resolved. See here[1].
>
> Thanks. So the DT stuff predates the introduction of memblock_mark_nomap,
> that's why...
>
> By reading the discussions, [1] still looks a sensible patch on its own,
> independently from the issue Nicolas tried to solve. Any reason for not
> applying it?

As I mentioned in the thread, same patch with 2 different reasons. So
I just wanted a better commit message covering both.

Rob