On Fri, Oct 09, 2020 at 08:13:56AM +0200, Greg Kroah-Hartman wrote: > On Thu, Oct 08, 2020 at 07:16:40PM +0100, Qais Yousef wrote: > > When the CONFIG_ASYMMETRIC_AARCH32 option is enabled (EXPERT), the type > > of the ARM64_HAS_32BIT_EL0 capability becomes WEAK_LOCAL_CPU_FEATURE. > > The kernel will now return true for system_supports_32bit_el0() and > > checks 32-bit tasks are affined to AArch32 capable CPUs only in > > do_notify_resume(). If the affinity contains a non-capable AArch32 CPU, > > the tasks will get SIGKILLed. If the last CPU supporting 32-bit is > > offlined, the kernel will SIGKILL any scheduled 32-bit tasks (the > > alternative is to prevent offlining through a new .cpu_disable feature > > entry). > > > > In addition to the relaxation of the ARM64_HAS_32BIT_EL0 capability, > > this patch factors out the 32-bit cpuinfo and features setting into > > separate functions: __cpuinfo_store_cpu_32bit(), > > init_cpu_32bit_features(). The cpuinfo of the booting CPU > > (boot_cpu_data) is now updated on the first 32-bit capable CPU even if > > it is a secondary one. The ID_AA64PFR0_EL0_64BIT_ONLY feature is relaxed > > to FTR_NONSTRICT and FTR_HIGHER_SAFE when the asymmetric AArch32 support > > is enabled. The compat_elf_hwcaps are only verified for the > > AArch32-capable CPUs to still allow hotplugging AArch64-only CPUs. > > > > Make sure that KVM never sees the asymmetric 32bit system. Guest can > > still ignore ID registers and force run 32bit at EL0. > > > > Co-developed-by: Qais Yousef <qais.yousef@xxxxxxx> > > Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> > > Signed-off-by: Qais Yousef <qais.yousef@xxxxxxx> > > --- > > arch/arm64/Kconfig | 14 ++++++ > > arch/arm64/include/asm/cpu.h | 2 + > > arch/arm64/include/asm/cpucaps.h | 3 +- > > arch/arm64/include/asm/cpufeature.h | 20 +++++++- > > arch/arm64/include/asm/thread_info.h | 5 +- > > arch/arm64/kernel/cpufeature.c | 66 +++++++++++++++----------- > > arch/arm64/kernel/cpuinfo.c | 71 ++++++++++++++++++---------- > > arch/arm64/kernel/process.c | 17 +++++++ > > arch/arm64/kernel/signal.c | 18 +++++++ > > arch/arm64/kvm/arm.c | 5 +- > > arch/arm64/kvm/guest.c | 2 +- > > arch/arm64/kvm/sys_regs.c | 14 +++++- > > 12 files changed, 176 insertions(+), 61 deletions(-) > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index 6d232837cbee..591853504dc4 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -1868,6 +1868,20 @@ config DMI > > > > endmenu > > > > +config ASYMMETRIC_AARCH32 > > + bool "Allow support for asymmetric AArch32 support" > > + depends on COMPAT && EXPERT > > Why EXPERT? You don't want this able to be enabled by anyone? TBH, I'd be inclined to drop the Kconfig option altogether. We're not looking at a lot of code here, so all it does is further fragment the build testing we get from CI (or it just ends up being enabled all of the time). A cmdline option, on the other hand, makes a tonne of sense to me, as it acts as an "opt-in" that the distribution is ready to handle the madness (because userspace will need to care about this even with the scheduler hacks proposed here). Will
