On Wed, Oct 28, 2020 at 09:37:46AM +0100, Greg Kroah-Hartman wrote:
> On Tue, Oct 27, 2020 at 09:51:17PM +0000, Will Deacon wrote:
> > Since 32-bit applications will be killed if they are caught trying to
> > execute on a 64-bit-only CPU in a mismatched system, advertise the set
> > of 32-bit capable CPUs to userspace in sysfs.
> >
> > Signed-off-by: Will Deacon <will@xxxxxxxxxx>
> > ---
> > .../ABI/testing/sysfs-devices-system-cpu | 8 ++++++++
> > arch/arm64/kernel/cpufeature.c | 19 +++++++++++++++++++
> > 2 files changed, 27 insertions(+)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > index b555df825447..19893fb8e870 100644
> > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > @@ -472,6 +472,14 @@ Description: AArch64 CPU registers
> > 'identification' directory exposes the CPU ID registers for
> > identifying model and revision of the CPU.
> >
> > +What: /sys/devices/system/cpu/aarch32_el0
> > +Date: October 2020
> > +Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>
> > +Description: Identifies the subset of CPUs in the system that can execute
> > + AArch32 (32-bit ARM) applications. If absent, then all or none
> > + of the CPUs can execute AArch32 applications and execve() will
> > + behave accordingly.
>
> How is this value represented? A hint here would be nice.
It's in the same format as
/sys/devices/system/cpu/{online,offline,possible,present}, so I'll just say
that (although the text for those doesn't seem to specify it either...).
> > What: /sys/devices/system/cpu/cpu#/cpu_capacity
> > Date: December 2016
> > Contact: Linux kernel mailing list <linux-kernel@xxxxxxxxxxxxxxx>
> > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > index 2e2219cbd54c..9f29d4d1ef7e 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -67,6 +67,7 @@
> > #include <linux/crash_dump.h>
> > #include <linux/sort.h>
> > #include <linux/stop_machine.h>
> > +#include <linux/sysfs.h>
> > #include <linux/types.h>
> > #include <linux/mm.h>
> > #include <linux/cpu.h>
> > @@ -1236,6 +1237,24 @@ bool system_has_mismatched_32bit_el0(void)
> > return fld == ID_AA64PFR0_EL0_64BIT_ONLY;
> > }
> >
> > +static ssize_t aarch32_el0_show(struct kobject *kobj,
> > + struct kobj_attribute *attr, char *buf)
> > +{
> > + const struct cpumask *mask = system_32bit_el0_cpumask();
> > + return sprintf(buf, "%*pbl\n", cpumask_pr_args(mask));
>
> sysfs_emit()?
>
> And a blank line to make checkpatch.pl happy :)
Hehe, yeah ok.
> > +}
> > +static const struct kobj_attribute aarch32_el0_attr = __ATTR_RO(aarch32_el0);
>
> DEVICE_ATTR_RO()?
>
> > +
> > +static int __init aarch32_el0_sysfs_init(void)
> > +{
> > + if (!__allow_mismatched_32bit_el0)
> > + return 0;
> > +
> > + return sysfs_create_file(&cpu_subsys.dev_root->kobj,
> > + &aarch32_el0_attr.attr);
>
> device_create_file() please, dev_root is a struct device, no need to
> "thunk" down to a "raw" sysfs call.
Totally missed I had a struct device in my hand, so hopefully that will tidy
things up a little bit.
Cheers,
Will
