On Thu, Jun 06, 2019 at 02:36:08PM -0300, Claudio Carvalho wrote: > This feature tells if the ultravisor firmware is available to handle > ucalls. Everything in this patch that depends on CONFIG_PPC_UV should just depend on CONFIG_PPC_POWERNV instead. The reason is that every host kernel needs to be able to do the ultracall to set partition table entry 0, in case it ends up being run on a machine with an ultravisor. Otherwise we will have the situation where a host kernel may crash early in boot just because the machine it's booted on happens to have an ultravisor running. The crash will be a particularly nasty one because it will happen before we have probed the machine type and initialized the console; therefore it will just look like the machine hangs for no discernable reason. We also need to think about how to provide a way for petitboot to know whether the kernel it is booting knows how to do a ucall to set its partition table entry. One suggestion would be to modify vmlinux.lds.S to add a new PT_NOTE entry in the program header of the binary with (say) a 64-bit doubleword which is a bitmap indicating capabilities of the binary. We would define the first bit as indicating that the kernel knows how to run under an ultravisor. When running under an ultravisor, petitboot could then look for the PT_NOTE and the ultravisor-capable bit in it, and if the PT_NOTE is not there or the bit is zero, put up a dialog warning the user that the kernel will probably crash early in boot, and asking for explicit confirmation that the user wants to proceed. Paul.
