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Date:   Thu, 4 Mar 2021 15:17:34 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc:     Jing Xiangfeng <jingxiangfeng@huawei.com>, catalin.marinas@arm.com,
        will@kernel.org, akpm@linux-foundation.org,
        paul.walmsley@sifive.com, palmer@dabbelt.com,
        aou@eecs.berkeley.edu, rppt@kernel.org, lorenzo.pieralisi@arm.com,
        guohanjun@huawei.com, sudeep.holla@arm.com, rjw@rjwysocki.net,
        lenb@kernel.org, song.bao.hua@hisilicon.com, ardb@kernel.org,
        anshuman.khandual@arm.com, bhelgaas@google.com, guro@fb.com,
        robh+dt@kernel.org, stable@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, frowand.list@gmail.com,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-riscv@lists.infradead.org,
        wangkefeng.wang@huawei.com
Subject: Re: [PATCH stable v5.10 0/7] arm64: Default to 32-bit wide ZONE_DMA
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References: <20210303073319.2215839-1-jingxiangfeng@huawei.com>
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On Thu, Mar 04, 2021 at 03:05:32PM +0100, Nicolas Saenz Julienne wrote:
> Hi Greg.
> 
> 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 an
> > > attempt go back to a saner default.
> > 
> > What problem does this solve?  How does this fit into the stable kernel
> > rules?
> 
> 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 allocate
> 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 creation is
> skipped.

What kernel/commit caused this "breakage"?

thanks,

greg k-h