On Wed, 2022-02-09 at 00:33 +0000, Andre Przywara wrote:
On Tue, 8 Feb 2022 22:05:00 +0000 Joakim Tjernlund Joakim.Tjernlund@infinera.com wrote:
Hi Joakim,
Trying to figure out how I should map the MMU for normal RAM so it acessible from all ELx security states.
^^^^^^^This does not make much sense. U-Boot is typically running in one exception level only, and sets up the page table for exactly that EL. Each EL uses a separate translation regime (with some twists for stage 2 EL2 and combined EL1/0, plus VHE). If you map your memory in EL3, then drop to EL2, the EL3 page tables become irrelevant.
So in U-Boot we just set up the page tables for the EL we are running in, and leave the paging for the lower exception levels to be set up at the discretion of our payloads (kernels, hypervisors).
Please not that *secure* memory is a separate concept, and handled by external hardware, typically using regions, not page tables.
I am a beginner w.r.t ARM and Secure/Non secure so thank you for above.
The problem I have is that I boot a custom SOC into u-boot and when u-boot tries to boot linux I get an error exception when u-boot calls armv8_switch_to_el2 to enter linux. I think the exception means "Instruction Abort taken without a change in Exception level." I was thinking it could be some privilege missing in MMU map. Note that kernel boots from a different memory region than u-boot but those two regions are mapped the same way.
Jocke
PS. I can cheat/hack u-boot to branch to the linux kernel address and that works until kernel tries to switch EL.
So far I have this mem_map:
/* memory mapped RAM. 32MB */ .virt = 0x60000000UL, .phys = 0x60000000UL, .size = 0x02000000UL, .attrs = PTE_BLOCK_MEMTYPE(MT_NORMAL) | PTE_BLOCK_INNER_SHAREbut starting to doubt that is correct, can someone suggest what to put in the .attrs field?
Those are the correct attributes for normal ("cache-able") memory. However you probably need at least another mapping for MMIO accesses, which MUST NOT be cacheable (MT_DEVICE_NGNRNE), but device memory. See the beginning of arch/arm/mach-sunxi/board.c for an example.
Cheers, Andre