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Subject: Re: [PATCH stable v5.10 0/7] arm64: Default to 32-bit wide ZONE_DMA
From:   Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Jing Xiangfeng <jingxiangfeng@huawei.com>, catalin.marinas@arm.com,
        will@kernel.org, akpm@linux-foundation.org,
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Date:   Thu, 04 Mar 2021 16:09:28 +0100
In-Reply-To: <YEDr/lYZHew88/Ip@kroah.com>
References: <20210303073319.2215839-1-jingxiangfeng@huawei.com>
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On Thu, 2021-03-04 at 15:17 +0100, Greg KH wrote:
> On Thu, Mar 04, 2021 at 03:05:32PM +0100, Nicolas Saenz Julienne wrote:
> > Hi Greg.
> >=20
> > On Thu, 2021-03-04 at 14:46 +0100, Greg KH wrote:
> > > On Wed, Mar 03, 2021 at 03:33:12PM +0800, Jing Xiangfeng wrote:
> > > > Using two distinct DMA zones turned out to be problematic. Here's a=
n
> > > > attempt go back to a saner default.
> > >=20
> > > What problem does this solve?  How does this fit into the stable kern=
el
> > > rules?
> >=20
> > We changed the way we setup memory zones in arm64 in order to cater for
> > Raspberry Pi 4's weird DMA constraints: ZONE_DMA spans the lower 1GB of=
 memory
> > and ZONE_DMA32 the rest of the 32bit address space. Since you can't all=
ocate
> > memory that crosses zone boundaries, this broke crashkernel allocations=
 on big
> > machines. This series fixes all this by parsing the HW description and =
checking
> > for DMA constrained buses. When not found, the unnecessary zone creatio=
n is
> > skipped.
>=20
> What kernel/commit caused this "breakage"?

1a8e1cef7603 arm64: use both ZONE_DMA and ZONE_DMA32

Regards,
Nicolas


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