linux-kernel - Re: [PATCH stable v5.10 0/7] arm64: Default to 32-bit wide ZONE

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Message-ID: <YEDr/lYZHew88/Ip@kroah.com>
Date:   Thu, 4 Mar 2021 15:17:34 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     Jing Xiangfeng <jingxiangfeng@...wei.com>, catalin.marinas@....com,
        will@...nel.org, akpm@...ux-foundation.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, rppt@...nel.org, lorenzo.pieralisi@....com,
        guohanjun@...wei.com, sudeep.holla@....com, rjw@...ysocki.net,
        lenb@...nel.org, song.bao.hua@...ilicon.com, ardb@...nel.org,
        anshuman.khandual@....com, bhelgaas@...gle.com, guro@...com,
        robh+dt@...nel.org, stable@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, frowand.list@...il.com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-riscv@...ts.infradead.org,
        wangkefeng.wang@...wei.com
Subject: Re: [PATCH stable v5.10 0/7] arm64: Default to 32-bit wide ZONE_DMA

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