> On Oct 12, 2022, at 11:38 AM, Edgecombe, Rick P <rick.p.edgecombe@xxxxxxxxx> wrote: > > On Wed, 2022-10-12 at 05:37 +0000, Song Liu wrote: >>> Then you have code that operates on module text like: >>> if (is_vmalloc_or_module_addr(addr)) >>> pfn = vmalloc_to_pfn(addr); >>> >>> It looks like it would work (on x86 at least). Should it be >>> expected >>> to? >>> >>> Especially after this patch, where there is memory that isn't even >>> tracked by the original vmap_area trees, it is pretty much a >>> separate >>> allocator. So I think it might be nice to spell out which other >>> vmalloc >>> APIs work with these new functions since they are named "vmalloc". >>> Maybe just say none of them do. >> >> I guess it is fair to call this a separate allocator. Maybe >> vmalloc_exec is not the right name? I do think this is the best >> way to build an allocator with vmap tree logic. > > Yea, I don't know about the name. I think someone else suggested it > specifically, right? I think Luis suggested rename module_alloc to vmalloc_exec. But I guess we still need module_alloc for module data allocations. > > I had called mine perm_alloc() so it could also handle read-only and > other permissions. What are other permissions that we use? We can probably duplicate the free_text_are_ tree logic for other cases. > If you keep vmalloc_exec() it needs some big > comments about which APIs can work with it, and an audit of the > existing code that works on module and JIT text. > >> >>> >>> >>> Separate from that, I guess you are planning to make this limited >>> to >>> certain architectures? It might be better to put logic with >>> assumptions >>> about x86 boot time page table details inside arch/x86 somewhere. >> >> Yes, the architecture need some text_poke mechanism to use this. > > It also depends on the space between _etext and the PMD aligned _etext > to be present and not get used by anything else. For other > architectures, there might be rodata there or other things. Good point! We need to make sure this part is not used by other things. > >> On BPF side, x86_64 calls this directly from arch code (jit engine), >> so it is mostly covered. For modules, we need to handle this better. > > That old RFC has some ideas around this. I kind of like your > incremental approach though. To me it seems to be moving in the right > direction. Thanks! Song
