> On 4 Jun 2020, at 09:59, Julien Grall <jul...@xen.org> wrote: > > > > On 04/06/2020 09:02, Bertrand Marquis wrote: >> Hi, > > Hi Bertrand, > >>> On 3 Jun 2020, at 19:09, Julien Grall <jul...@xen.org> wrote: >>> >>> >>> >>> On 03/06/2020 18:13, CodeWiz2280 wrote: >>>> Hi Julien, >>> >>> Hello, >>> >>> In general, we avoid top post on xen-devel, instead we reply inline. I >>> believe gmail should allow you to do it :). >>> >>>> The offset is already applied to the memory nodes in the device tree, >>>> meaning a direct Linux boot from uboot would have only the 36-bit >>>> addresses in the device tree (0x8_0000_0000 and 0x8_8000_0000). Linux >>>> would start executing from a 32-bit address space however and then switch >>>> over to the aliased 36-bit addresses in the device tree as discussed below >>>> by early_paging_init(). >>>> I had to add the 32-bit memory node 0x8000_0000 in uboot in place of the >>>> 0x8_0000_0000 node otherwise Xen would detect the 32-bit processor and >>>> panic on "Unable to detect the first memory bank" in domain_build.c. >>> >>> So for 32-bit Xen requires to have the first bank below 4GB. This is >>> because you can't boot from a physical address above 32-bit. >>> >>> Obviously, this check wouldn't work on your platform because all your >>> memory will be above 4GB. >> I think that the Keystone board has low memory accessible at 2 different >> address (one low and one high). >> I would here suggest to have a dtb with 2 regions (one under 4GB and one >> over) and remove from the region over 4G the area already addressed by the >> region under 4GB. > > I thought about this. However, in an earlier reply, David wrote: > > "4. The dom0 kernel will boot from xen if the early_paging_init switch step > is skipped, and the low mem stays in 32-bit....but there is a > problem with the peripherals so this is not an acceptable solution." > > It is not clear to me what sort of issues will arise with the peripherals. > But I have assumed that it wouldn't be possible for Dom0 to keep using the > memory below 4GB.
I would have thought that linux would have need some memory, even small in the 32bit space in order to boot. I could understand that some memory in the low address space needs to be reserved by Linux as DMA area for peripherals not supporting 36-bit addresses, but the whole low memory sounds like a big restriction. Would it be possible to have a bit more information on the “problem with peripherals” here ? Cheers Bertrand
