On Wed, Oct 04, 2017 at 12:32:07PM +0100, Dave P Martin wrote: > On Wed, Oct 04, 2017 at 12:10:40PM +0100, Catalin Marinas wrote: > > On Wed, Oct 04, 2017 at 11:14:26AM +0100, Mark Rutland wrote: > > > On Wed, Oct 04, 2017 at 10:48:05AM +0100, Suzuki K Poulose wrote: > > > > Make sure the MRS emulation is enabled early enough, such that the > > > > early userspace applications (e.g, those run from initrd) could > > > > use the facility without crashing them. > > > > > > > > Fixes: commit 77c97b4ee2129 ("arm64: cpufeature: Expose CPUID registers by emulation") > > > > Reported-by: Matwey V. Kornilov <matwey.kornilov@xxxxxxxxx> > > > > Cc: James Morse <james.morse@xxxxxxx> > > > > Cc: Dave Martin <Dave.martin@xxxxxxx> > > > > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > > > > Cc: Will Deacon <will.deacon@xxxxxxx> > > > > Cc: stable@xxxxxxxxxxxxxxx > > > > Cc: Mark Rutland <mark.rutland@xxxxxxx> > > > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx> > > > > > > This looks sensible, but shouldn't we do the same for other > > > late_inicalls can affect initrd userspace? > > > > > > e.g. armv8_deprecated_init, fpsimd_init, sys_reg_genericv8_init? > > > > I think we should, though not all of them are concerned with the user > > code. For example, fpsimd_init() takes care of the pm/hotplug aspect and > > nothing to do with user space. That said, making it core_initcall() is > > probably not a bad thing (just a statement that it is concerned with the > > core initialisation), as long as all the other infrastructure it > > registers with is up. > > > > For Suzuki's patch, I was thinking of enabling emulation before we > > register the HWCAP_CPUID bit (setup_elf_hwcaps). However, that means we > > have to bring it before smp_cpus_done(). It's not really worth it as we > > don't expect any user space at that point. > > I don't think the hwcaps shouldn't change after entry to userspace, > so it really doesn't matter whether HWCAP_CPUID is set before or > after registration: for userspace it should all already have happened. Good point, I forgot about this. > It looks to me like all initcalls are called in the same kernel thread > that execs the initramfs init process, before the exec. > > So I still don't see how a built-in late initcall can not have been > called before entry to userspace. > > The patch seems to demonstrate that I'm wrong though. > What am I missing? I also wondered about this. I think is the kernel invoking modprobe before the actual init/linuxrc in an initrd. -- Catalin