Nathan Lynch <n...@pobox.com> wrote: > > Oren Laadan wrote: > > > > Nathan Lynch wrote: > > > > > > What doesn't work: > > > * restarting a 32-bit task from a 64-bit task and vice versa > > > > Is there a test to bail if we attempt to checkpoint such tasks ? > > No, but I'll add one if it looks too hard to fix for the next round.
Unfortunately, adding a check for this is hard. The "point of no return" in the restart path is cr_read_mm, which tears down current's address space. cr_read_mm runs way before cr_read_cpu, which is the only restart method I've implemented for powerpc so far. So, checking for this condition in cr_read_cpu is too late if I want restart(2) to return an error and leave the caller's memory map intact. (And I do want this: restart should be as robust as execve.) Well okay then, cr_read_head_arch seems to be the right place in the restart sequence for the architecture code to handle this. However, cr_write_head_arch (which produces the buffer that cr_read_head_arch consumes) is not provided a reference to the task to be checkpointed, nor can it assume that it's operating on current. I need a reference to a task before I can determine whether it's running in 32- or 64-bit mode, or using the FPU, Altivec, SPE, whatever. In any case, mixing 32- and 64-bit tasks across restart is something I eventually want to support, not reject. But the problem I've outlined applies to FPU state and vector extensions (VMX, SPE), as well as sanity-checking debug register (DABR) contents. We'll need to be able to error out gracefully from restart when a checkpoint image specifies a feature unsupported by the current kernel or hardware. But I don't see how to do it with the current architecture. Am I missing something? _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
