From: Ard Biesheuvel <ardb@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Linux ARM <linux-arm-kernel@lists.infradead.org>,
ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
Will Deacon <will@kernel.org>,
Jeremy Linton <jeremy.linton@arm.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
Rob Herring <robh+dt@kernel.org>, Christoph Hellwig <hch@lst.de>,
Robin Murphy <robin.murphy@arm.com>,
Hanjun Guo <guohanjun@huawei.com>,
Sudeep Holla <sudeep.holla@arm.com>,
Anshuman Khandual <anshuman.khandual@arm.com>
Subject: Re: [PATCH] arm64: mm: set ZONE_DMA size based on early IORT scan
Date: Mon, 12 Oct 2020 16:19:08 +0200 [thread overview]
Message-ID: <CAMj1kXEmAxytDjcAgpGpCqWcEuO0HijLVuTZcz-vywW=a74mmA@mail.gmail.com> (raw)
In-Reply-To: <20201012112453.GD9844@gaia>
On Mon, 12 Oct 2020 at 13:24, Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Mon, Oct 12, 2020 at 12:43:05PM +0200, Ard Biesheuvel wrote:
> > On Mon, 12 Oct 2020 at 11:30, Ard Biesheuvel <ardb@kernel.org> wrote:
> > > On Mon, 12 Oct 2020 at 11:28, Catalin Marinas <catalin.marinas@arm.com> wrote:
> > > > On Sat, Oct 10, 2020 at 11:31:53AM +0200, Ard Biesheuvel wrote:
> > > > > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > > > > index f0599ae73b8d..829fa63c3d72 100644
> > > > > --- a/arch/arm64/mm/init.c
> > > > > +++ b/arch/arm64/mm/init.c
> > > > > @@ -191,6 +191,14 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
> > > > > unsigned long max_zone_pfns[MAX_NR_ZONES] = {0};
> > > > >
> > > > > #ifdef CONFIG_ZONE_DMA
> > > > > + if (IS_ENABLED(CONFIG_ACPI)) {
> > > > > + extern unsigned int acpi_iort_get_zone_dma_size(void);
> > > >
> > > > Nitpick: can we add this prototype to include/linux/acpi_iort.h?
> > > >
> > > > > +
> > > > > + zone_dma_bits = min(zone_dma_bits,
> > > > > + acpi_iort_get_zone_dma_size());
> > > > > + arm64_dma_phys_limit = max_zone_phys(zone_dma_bits);
> > > > > + }
> > > > > +
> > > > > max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit);
> > > >
> > > > I think we should initialise zone_dma_bits slightly earlier via
> > > > arm64_memblock_init(). We'll eventually have reserve_crashkernel()
> > > > called before this and it will make use of arm64_dma_phys_limit for
> > > > "low" reservations:
> > > >
> > > > https://lore.kernel.org/linux-arm-kernel/20200907134745.25732-7-chenzhou10@huawei.com/
> > > >
> > >
> > > We don't have access to the ACPI tables yet at that point.
> >
> > Also, could someone give an executive summary of why it matters where
> > the crashkernel is loaded? As far as I can tell, reserve_crashkernel()
> > only allocates memory for the kernel's executable image itself, which
> > can usually be loaded anywhere in memory. I could see how a
> > crashkernel might need some DMA'able memory if it needs to use the
> > hardware, but I don't think that is what is going on here.
>
> I thought the crashkernel needs some additional reserved RAM as well to
> be able to run. It should not touch the original kernel's memory as it
> usually needs to dump it.
>
Looking at the code, it is definitely allocating memory for the kernel
itself (as it refers to the 2 MB alignment requirement), and given
that we used to require the kernel to be at the base of the linear
region to even be able to access all of memory, I suspect that we
might be able to relax this requirement. Not sure what that means for
the userland tools, though.
next prev parent reply other threads:[~2020-10-12 14:19 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-10 9:31 [PATCH] arm64: mm: set ZONE_DMA size based on early IORT scan Ard Biesheuvel
2020-10-12 9:28 ` Catalin Marinas
2020-10-12 9:30 ` Ard Biesheuvel
2020-10-12 10:43 ` Ard Biesheuvel
2020-10-12 11:24 ` Catalin Marinas
2020-10-12 14:19 ` Ard Biesheuvel [this message]
2020-10-12 15:49 ` Catalin Marinas
2020-10-12 15:55 ` Ard Biesheuvel
2020-10-12 16:22 ` Catalin Marinas
2020-10-12 16:35 ` Ard Biesheuvel
2020-10-12 16:59 ` Catalin Marinas
2020-10-13 14:42 ` Nicolas Saenz Julienne
2020-10-13 15:45 ` Catalin Marinas
2020-10-14 12:44 ` Ard Biesheuvel
2020-10-14 12:54 ` Nicolas Saenz Julienne
2020-10-12 12:16 ` kernel test robot
2020-10-13 11:09 ` Lorenzo Pieralisi
2020-10-13 11:22 ` Ard Biesheuvel
2020-10-13 11:38 ` Ard Biesheuvel
2020-10-13 11:43 ` Ard Biesheuvel
2020-10-13 13:13 ` Lorenzo Pieralisi
2020-10-13 13:42 ` Ard Biesheuvel
2020-10-13 15:11 ` Robin Murphy
2020-10-13 15:41 ` Lorenzo Pieralisi
2020-10-14 16:18 ` Catalin Marinas
2020-10-14 17:23 ` Lorenzo Pieralisi
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