On Mon, Jan 30, 2023 at 10:53:28AM +0000, Lad, Prabhakar wrote: > > > To avoid this the ILM/DLM memory regions are now added to the root > > > domain region of the PMPU with permissions set to 0x0 for S/U modes so > > > that any access to these regions gets blocked and for M-mode we grant > > > full access (R/W/X). This prevents any users from accessing these > > > regions by triggering an unhandled signal 11 in S/U modes. > > > > I have no idea what any of this means. > > > Basically we are making use of the memory protection unit (MPU) so > that only M-mode is allowed to access this region and S/U modes are > blocked. This sounds like RISC-V terminology. I have no idea what M, S or U modes are (Supervisor and User, I'd guess for the last two?) > > > This works as expected but for applications say for example when doing > > > mmap to this region would still succeed and later down the path when > > > doing a read/write to this location would cause unhandled signal 11. > > > To handle this case gracefully we might want mmap() itself to fail if > > > the addr/offset falls in this local memory region. > > > > No, that's not what you want. You want mmap to avoid allocating address > > space in that virtual address range. I don't know if we have a good > > way to do that at the moment; like I said I've never seen such broken > > hardware before. > > > > I'd say the right way to solve this is to add a new special kind of VMA > > to the address space that covers this range. > Do you have any pointers where I can look further into this? Before we go too deeply into it, how much would it cost to buy all of these parts and feed them into a shredder? I'm not entirely joking; if it's less than the software engineering time it'd take to develop and support this feature, we should do it.
