On Wed, Nov 28, 2018 at 11:27:17AM -0800, David Miller wrote: > From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > 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. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up
