Effective and correct way of invalidating data-cache for arm64 Xen domain

[xakep-amatop]

If we build Zephyr as a Xen Initial domain or for xenvm board, it won't work with cache management support enabled. Initialization of board(s) is failed in enable_mmu_el1 function during call sys_cache_data_invd_all --- this call has set/way instructions. Unfortunately, set/way ops are not easily virtualized by Xen. S/W emulation is disabled, because IP-MMU is active for Dom0. IP-MMU is a IO-MMU made by Renesas, as any good IO-MMU, it shares page-tables with CPU. Trying to emulate S/W with IP-MMU active will lead to IO-MMU faults.

Our team have found a fast workaround for the issue: just replace sys_cache_data_invd_all call with the next one sys_cache_data_invd_range((void *)CONFIG_KERNEL_VM_BASE, CONFIG_KERNEL_VM_SIZE). But this approach may take long time during the initialization of the board --- the larger the virtual memory size we have, the longer the function works.

So, the question is:
Is there a way to invalidate dcache more effectively without using set/way instructions?

[lorc]

FYI, U-boot had the same issue and there is the fix they implemented: https://www.mail-archive.com/u-boot@lists.denx.de/msg464402.html

[lorc]

While this worked well for U-Boot, I am not sure that this is the best approach for Zephyr.

IMO, it is better to clean/invalidate every page during mapping.