> https://lore.kernel.org/lkml/45a2f0b8-5bac-8b5d-d595-f92e9acb27ad@xxxxxxx > > + /* Map relocation function va == pa */ > > + rc = trans_pgd_map_page(&info, trans_ttbr0, __va(kern_reloc), > > + kern_reloc, PAGE_KERNEL_EXEC); > > + if (rc) > > + return rc; > James wrote: > You can't do this with the page table helpers. We support platforms > with no memory in range of TTBR0's VA space. See dd006da21646f > > You will need some idmapped memory to turn the MMU off on a system > that booted at EL1. This will need to be in a set of page tables > that the helpers can't easily touch - so it should only be a single > page. (like the arch code's existing idmap - although that may > have been overwritten). > > (I have a machine where this is a problem, if I get the time I will > have a stab at making hibernate's safe page idmaped). > --- > > As I understand, there are platforms where TTBR0 cannot include all > physical memory for idmap. However, kexec must have at least one page > idmapped (kimage->control_code_page) to be able to relocate kernel > while MMU is enabled: > > I am still trying to fully understand the problem: > CONFIG_ARM64_VA_BITS must be smaller than 48 and physical memory must > start at a high address for this problem to occur. > > Why can't we simply decrease T0SZ to cover all physical memory? Is there a way to reproduce this platform with qemu? Pasha
