From mboxrd@z Thu Jan 1 00:00:00 1970 From: Suzuki.Poulose@arm.com (Suzuki K Poulose) Date: Mon, 22 Jan 2018 15:13:06 +0000 Subject: [PATCH v2 1/6] arm64: cpufeature: Allow early detect of specific features In-Reply-To: <5cafee50-c2ee-6c04-756c-785cdf822b27@arm.com> References: <1516190084-18978-1-git-send-email-julien.thierry@arm.com> <1516190084-18978-2-git-send-email-julien.thierry@arm.com> <2f2a406b-fddf-6c30-4052-650f57ac317a@arm.com> <2fa17395-d268-5ec9-6033-08ecb7eba44a@arm.com> <5cafee50-c2ee-6c04-756c-785cdf822b27@arm.com> Message-ID: <4a8dc4ec-2762-e1cd-8126-ff44abcb67f2@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 22/01/18 15:01, Julien Thierry wrote: > > > On 22/01/18 14:45, Suzuki K Poulose wrote: >> On 22/01/18 12:21, Julien Thierry wrote: >>> >>> >>> On 22/01/18 12:05, Suzuki K Poulose wrote: >>>> On 17/01/18 11:54, Julien Thierry wrote: >>>>> From: Daniel Thompson >>>>> >>>>> Currently it is not possible to detect features of the boot CPU >>>>> until the other CPUs have been brought up. >>>>> >>>>> This prevents us from reacting to features of the boot CPU until >>>>> fairly late in the boot process. To solve this we allow a subset >>>>> of features (that are likely to be common to all clusters) to be >>>>> detected based on the boot CPU alone. >>>>> >>>>> Signed-off-by: Daniel Thompson >>>>> [julien.thierry at arm.com: check non-boot cpu missing early features, avoid >>>>> ???????????? duplicates between early features and normal >>>>> ???????????? features] >>>>> Signed-off-by: Julien Thierry >>>>> Cc: Catalin Marinas >>>>> Cc: Will Deacon >>>>> Cc: Suzuki K Poulose >>>>> --- >>>>> ? arch/arm64/kernel/cpufeature.c | 69 ++++++++++++++++++++++++++++-------------- >>>>> ? 1 file changed, 47 insertions(+), 22 deletions(-) >>>>> >>>>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c >>>>> index a73a592..6698404 100644 >>>>> --- a/arch/arm64/kernel/cpufeature.c >>>>> +++ b/arch/arm64/kernel/cpufeature.c >>>>> @@ -52,6 +52,8 @@ >>>>> ? DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS); >>>>> ? EXPORT_SYMBOL(cpu_hwcaps); >>>>> >>>>> +static void __init setup_early_feature_capabilities(void); >>>>> + >>>>> ? /* >>>>> ?? * Flag to indicate if we have computed the system wide >>>>> ?? * capabilities based on the boot time active CPUs. This >>>>> @@ -542,6 +544,8 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info) >>>>> ????????? init_cpu_ftr_reg(SYS_ZCR_EL1, info->reg_zcr); >>>>> ????????? sve_init_vq_map(); >>>>> ????? } >>>>> + >>>>> +??? setup_early_feature_capabilities(); >>>>> ? } >>>>> >>>>> ? static void update_cpu_ftr_reg(struct arm64_ftr_reg *reg, u64 new) >>>>> @@ -846,7 +850,7 @@ static bool has_no_fpsimd(const struct arm64_cpu_capabilities *entry, int __unus >>>>> ????????????????????? ID_AA64PFR0_FP_SHIFT) < 0; >>>>> ? } >>>>> >>>>> -static const struct arm64_cpu_capabilities arm64_features[] = { >>>>> +static const struct arm64_cpu_capabilities arm64_early_features[] = { >>>>> ????? { >>>>> ????????? .desc = "GIC system register CPU interface", >>>>> ????????? .capability = ARM64_HAS_SYSREG_GIC_CPUIF, >>>>> @@ -857,6 +861,10 @@ static bool has_no_fpsimd(const struct arm64_cpu_capabilities *entry, int __unus >>>>> ????????? .sign = FTR_UNSIGNED, >>>>> ????????? .min_field_value = 1, >>>>> ????? }, >>>>> +??? {} >>>>> +}; >>>>> + >>>> >>>> >>>> Julien, >>>> >>>> One potential problem with this is that we don't have a way >>>> to make this work on a "theoretical" system with and without >>>> GIC system reg interface. i.e, if we don't have the CONFIG >>>> enabled for using ICC system regs for IRQ flags, the kernel >>>> could still panic. I understand this is not a "normal" configuration >>>> but, may be we could make the panic option based on whether >>>> we actually use the system regs early enough ? >>>> >>> >>> I see, however I'm not sure what happens in the GIC drivers if we have a CPU running with a GICv3 and other CPUs with something else... But of course this is not technically limited by the arm64 capabilities handling. >>> >>> What behaviour would you be looking for? A way to prevent the CPU to be brought up instead of panicking? >>> >> >> If we have the CONFIG enabled for using system regs, we can continue >> to panic the system. Otherwise, we should ignore the mismatch early, >> as we don't use the system register access unless all boot time active >> CPUs have it. >> > > Hmmm, we use the CPUIF (if available) in the first CPU pretty much as soon as we re-enable interrupts in the GICv3 driver, which is way before the other CPUs are brought up. Isn't this CPUIF access an alternative, patched only when CPUIF feature enabled ? (which is done only after all the allowed SMP CPUs are brought up ) > > other CPUs get to die_early(). Really ? I thought only late CPUs are sent to die_early(). > >> In a nutshell, this is an early feature only if the CONFIG is enabled, >> otherwise should fall back to the normal behavior. >> > > Maybe we should just not panic and let the mismatching CPUs die. > It's a system wide feature and linux will try to make the other CPUs match the boot CPU's config anyway. > Suzuki