Messages in this thread | | | Date | Wed, 28 Nov 2018 19:47:09 +0000 | From | Russell King - ARM Linux <> | Subject | Re: remove the ->mapping_error method from dma_map_ops V2 |
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On Wed, Nov 28, 2018 at 11:27:17AM -0800, David Miller wrote: > From: Linus Torvalds <torvalds@linux-foundation.org> > Date: Wed, 28 Nov 2018 10:00:06 -0800 > > > Not all memory is accessible even to the kernel. If you have memory > > that shows up in the last page of phys_addr_t, you just mark it > > reserved at boot-time. > > It's not the physical memory at the end that needs to be reserved. > > It's the IOMMU mapping arena.
True, if and only if you have an IOMMU.
Where there isn't an IOMMU, then we'd have to reserve every page that that translates to a bus address in the top 4K of dma_addr_t on any bus in the system - that means knowing early in the kernel initialisation about all buses in the system so we can detect and reserve these pages.
I don't think that's trivial to do.
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