[ +linux-arm-kernel Context: This is regarding VMSPLIT_4G_4G support for 32-bit ARM as a possible replacement to highmem. For that, initially, it is being attempted to move static kernel mapping from lowmem to vmalloc space.
in next reply, i will remove everyone/list !ARM related ] Hi, On Sun, May 03, 2020 at 10:20:39PM +0200, Arnd Bergmann wrote: > Which SoC platform are you running this on? Just making > sure that this won't conflict with static mappings later. Versatile Express V2P-CA15 on qemu, qemu options include --smp 2 & 2GB memory. BTW, i could not convince myself why, except for DEBUG_LL, static io mappings are used. > > One problem I see immediately in arm_memblock_init() Earlier it went past arm_memblock_init(), issue was clearing the page tables from VMALLOC_START in devicemaps_init() thr' paging_init(), which was like cutting the sitting branch of the tree. Now it is crashing at debug_ll_io_init() of devicemap_init(), and printascii/earlycon was & is being used to debug :). Things are going wrong when it tries to create mapping for debug_ll. It looks like a conflict with static mapping, which you mentioned above, at the same time i am not seeing kernel static mapping in the same virtual address, need to dig deeper. Also tried removing DEBUG_LL, there is a deafening silence in the console ;) > is that it uses > __pa() to convert from virtual address in the linear map to physical, > but now you actually pass an address that is in vmalloc rather than > the linear map. __virt_to_phys_nodebug() which does the actual work on __pa() invocation has been modifed to handle that case (ideas lifted from ARM64's implementation), though currently it is a hack as below (and applicable only for ARM_PATCH_PHYS_VIRT disabled case), other hacks being VMALLOC_OFFSET set to 0 and adjusting vmalloc size. static inline phys_addr_t __virt_to_phys_nodebug(unsigned long x) { phys_addr_t __x = (phys_addr_t)x; if (__x >= 0xf0000000) return __x - KIMAGE_OFFSET + PHYS_OFFSET; else return __x - PAGE_OFFSET + PHYS_OFFSET; } Regards afzal