On 10/26/20 20:08, Greg Kroah-Hartman wrote: > On Mon, Oct 26, 2020 at 07:02:50PM +0000, Qais Yousef wrote: > > On 10/22/20 15:55, Greg Kroah-Hartman wrote: > > > On Thu, Oct 22, 2020 at 02:47:52PM +0100, Qais Yousef wrote: > > > > On 10/21/20 15:41, Will Deacon wrote: > > > > > > We already expose MIDR and REVIDR via the current sysfs interface. We > > > > > > can expand it to include _all_ the other ID_* regs currently available > > > > > > to user via the MRS emulation and we won't have to debate what a new > > > > > > interface would look like. The MRS emulation and the sysfs info should > > > > > > probably match, though that means we need to expose the > > > > > > ID_AA64PFR0_EL1.EL0 field which we currently don't. > > > > > > > > > > > > I do agree that an AArch32 cpumask is an easier option both from the > > > > > > kernel implementation perspective and from the application usability > > > > > > one, though not as easy as automatic task placement by the scheduler (my > > > > > > first preference, followed by the id_* regs and the aarch32 mask, though > > > > > > not a strong preference for any). > > > > > > > > > > If a cpumask is easier to implement and easier to use, then I think that's > > > > > what we should do. It's also then dead easy to disable if necessary by > > > > > just returning 0. The only alternative I would prefer is not having to > > > > > expose this information altogether, but I'm not sure that figuring this > > > > > out from MIDR/REVIDR alone is reliable. > > > > > > > > So the mask idea is about adding a new > > > > > > > > /sys/devices/system/cpu/aarch32_cpus > > > > > > > > ? > > > > > > Is this a file, a directory, or what? What's the contents? > > > > > > Without any of that, I have no idea if it's "ok" or not... > > > > Hopefully the below patch explains better. Note that I added the new attribute > > to driver/base/cpu.c, but assuming we will still want to go down this route, we > > will need a generic way for archs to add their attributes to > > /sys/devices/system/cpu/. > > > > Something like having a special define for archs to append their own > > attributes list > > > > #define SYSFS_SYSTEM_CPU_ARCH_ATTRIBUTES > > > > Or probably there's a way to add this file (attribute) dynamically from arch > > code that I just didn't figure out how to do yet. > > Please do that, sysfs files should not be present when the information > is not needed from them. Look at the is_visible() callback for the > attribute for how to do it. Okay, thanks for the hint. Will look at that. > > > > Thanks > > > > -- > > Qais Yousef > > > > > > ---------->8------------ > > > > >From 96dfdfdacb2a26a60ba19051e8c72e839eb5408b Mon Sep 17 00:00:00 2001 > > From: Qais Yousef <qais.yousef@xxxxxxx> > > Date: Mon, 26 Oct 2020 16:33:32 +0000 > > Subject: [PATCH] arm64: export aarch32_online mask in sysfs > > > > This patch to be applied on top of arm64 Asymmetric AArch32 support. > > > > It explores the option of exporting the AArch32 capable cpus as a mask > > on sysfs. > > > > This is to help drive the discussion on the API before sending the next > > version which I yet to address some of the review comments. > > > > The output looks like: > > > > # cat /sys/devices/system/cpu/aarch32_online > > 0-5 > > > > Signed-off-by: Qais Yousef <qais.yousef@xxxxxxx> > > --- > > Documentation/ABI/testing/sysfs-devices-system-cpu | 7 +++++++ > > arch/arm64/include/asm/cpufeature.h | 2 ++ > > arch/arm64/kernel/cpufeature.c | 8 ++++++++ > > drivers/base/cpu.c | 12 ++++++++++++ > > 4 files changed, 29 insertions(+) > > > > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu > > index b555df825447..9ccb5c3f5ee3 100644 > > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu > > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu > > @@ -36,6 +36,13 @@ Description: CPU topology files that describe kernel limits related to > > > > See Documentation/admin-guide/cputopology.rst for more information. > > > > +What: /sys/devices/system/cpu/aarch32_online > > +Date: October 2020 > > +Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx> > > +Description: CPU topology file that describes which cpus support AArch32 at > > + EL0. Only available on arm64. > > + > > + The value is updated when a cpu becomes online then sticks. > > What does "then sticks" mean? Was thinking like a sticky bit. When a cpu becomes online and we discover that it is aarch32 capable, we set the bit. But never clear it again if the cpu goes offline later. I'll reword it. > > > > > > What: /sys/devices/system/cpu/probe > > /sys/devices/system/cpu/release > > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h > > index 2b87f17b2bd4..edd18002ad81 100644 > > --- a/arch/arm64/include/asm/cpufeature.h > > +++ b/arch/arm64/include/asm/cpufeature.h > > @@ -380,6 +380,8 @@ cpucap_multi_entry_cap_matches(const struct arm64_cpu_capabilities *entry, > > return false; > > } > > > > +extern cpumask_t aarch32_el0_mask; > > + > > extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS); > > extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS]; > > extern struct static_key_false arm64_const_caps_ready; > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > > index 0f7307c8ad80..662bbc2b15cd 100644 > > --- a/arch/arm64/kernel/cpufeature.c > > +++ b/arch/arm64/kernel/cpufeature.c > > @@ -1723,6 +1723,13 @@ cpucap_panic_on_conflict(const struct arm64_cpu_capabilities *cap) > > return !!(cap->type & ARM64_CPUCAP_PANIC_ON_CONFLICT); > > } > > > > +cpumask_t aarch32_el0_mask; > > +static void cpu_enable_aarch32_el0(struct arm64_cpu_capabilities const *cap) > > +{ > > + if (has_cpuid_feature(cap, SCOPE_LOCAL_CPU)) > > + cpumask_set_cpu(smp_processor_id(), &aarch32_el0_mask); > > +} > > + > > static const struct arm64_cpu_capabilities arm64_features[] = { > > { > > .desc = "GIC system register CPU interface", > > @@ -1809,6 +1816,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = { > > { > > .capability = ARM64_HAS_ASYM_32BIT_EL0, > > .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE, > > + .cpu_enable = cpu_enable_aarch32_el0, > > .matches = has_cpuid_feature, > > .sys_reg = SYS_ID_AA64PFR0_EL1, > > .sign = FTR_UNSIGNED, > > diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c > > index d2136ab9b14a..569baacde508 100644 > > --- a/drivers/base/cpu.c > > +++ b/drivers/base/cpu.c > > @@ -459,6 +459,15 @@ EXPORT_SYMBOL_GPL(cpu_device_create); > > static DEVICE_ATTR(modalias, 0444, print_cpu_modalias, NULL); > > #endif > > > > +#ifdef CONFIG_ARM64 > > +static ssize_t print_aarch32_online(struct device *dev, > > + struct device_attribute *attr, char *buf) > > +{ > > + return cpumap_print_to_pagebuf(true, buf, &aarch32_el0_mask); > > +} > > +static DEVICE_ATTR(aarch32_online, 0444, print_aarch32_online, NULL); > > DEVICE_ATTR_RO()? Indeed. > > > +#endif > > Hah, no, no arch-specific stuff in here, sorry. Please do this properly > in your arch-specific code only. Of course. It was just to see this is okay. Let me figure out how to clean this up. Thanks! -- Qais Yousef