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Date:   Sun, 7 Mar 2021 16:24:31 +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,
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Subject: Re: [PATCH stable v5.10 0/7] arm64: Default to 32-bit wide ZONE_DMA
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On Thu, Mar 04, 2021 at 04:09:28PM +0100, Nicolas Saenz Julienne wrote:
> 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.
> > > 
> > > 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"?
> 
> 1a8e1cef7603 arm64: use both ZONE_DMA and ZONE_DMA32

Thanks for the info, all now queued up.

greg k-h