[PATCH stable v5.10 0/7] arm64: Default to 32-bit wide ZONE_DMA

Greg KH gregkh at linuxfoundation.org
Thu Mar 4 14:17:34 GMT 2021


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



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