[PATCH v3 05/12] arm64: smp: Defer RCU registration during secondary CPU bringup
Jinjie Ruan
ruanjinjie at huawei.com
Wed Jul 8 02:13:30 PDT 2026
On 7/7/2026 6:27 PM, Will Deacon wrote:
> Jinjie,
>
> On Tue, Jul 07, 2026 at 11:02:32AM +0800, Jinjie Ruan wrote:
>> On 7/7/2026 1:39 AM, Will Deacon wrote:
>>> ce3d31ad3cac ("arm64/smp: Move rcu_cpu_starting() earlier") was to
>>> handle the useless print in cpuinfo_detect_icache_policy(), but I've
>>> decided just to remove that one. So I think the remaining prints we have
>>> to worry about in this early boot code are from error paths in the
>>> CPU feature detection logic (check_local_cpu_capabilities()).
>>>
>>> Given that those error paths should all be fatal, perhaps we could
>>> rework cpu_die_early() and cpu_panic_kernel() as macros that take a
>>> string argument and either call printk_deferred() (similarly to what you
>>> suggested in a previous version of your series [1]) or do the
>>> lockdep_off() there before a pr_crit().
>>>
>>> What do you think?
>>
>> That is an excellent point. Reworking cpu_die_early() and
>> cpu_panic_kernel() to uniformly use printk_deferred() based on the
>> specific error type or the string argument is a much cleaner approach.
>>
>> This makes perfect sense because these paths are inherently fatal, and
>> switching to deferred printing avoids the risky lock-taking and RCU
>> runtime constraints during early boot entirely. It cleanly resolves the
>> diagnostic noise without broadly blinding lockdep or hiding potential
>> locking issues down the line.
>>
>> I fully agree with this approach.
>
> It's great that your AI chatbot thinks this is fantastic, but what do
> _you_ think? I'm much more interested in your opinion, as you have
> already spent time thinking about this.
Sorry, I had AI polish the language based on my ideas, but the main
points are consistent.
My main concern is that future new features might add printing in the
check_local_cpu_capabilities() function. How can we enforce them to only
use the defer version of printk or the new macro we define?
Is what you referring to similar to the following implementation?
diff --git a/arch/arm64/include/asm/cpufeature.h
b/arch/arm64/include/asm/cpufeature.h
index a57870fa96db..6c95227032b0 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -26,6 +26,18 @@
#include <linux/kernel.h>
#include <linux/cpumask.h>
+#define cpu_panic_kernel_with_msg(fmt, ...) \
+do { \
+ printk_deferred(KERN_CRIT pr_fmt(fmt), ##__VA_ARGS__); \
+ cpu_panic_kernel(); \
+} while (0)
+
+#define cpu_die_early_with_msg(fmt, ...) \
+do { \
+ printk_deferred(KERN_CRIT pr_fmt(fmt), ##__VA_ARGS__); \
+ cpu_die_early(); \
+} while (0)
+
/*
* CPU feature register tracking
*
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 1a426725265c..20f00819c1cb 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -3699,14 +3699,17 @@ static void verify_local_cpu_caps(u16 scope_mask)
}
if (i < ARM64_NCAPS) {
- pr_crit("CPU%d: Detected conflict for capability %d
(%s), System: %d, CPU: %d\n",
- smp_processor_id(), caps->capability,
- caps->desc, system_has_cap, cpu_has_cap);
+ #define CAP_CONFLICT_FMT "CPU%d: Detected conflict for
capability %d (%s), System: %d, CPU: %d\n"
if (cpucap_panic_on_conflict(caps))
- cpu_panic_kernel();
+ cpu_panic_kernel_with_msg(CAP_CONFLICT_FMT,
+ smp_processor_id(),
caps->capability,
+ caps->desc,
system_has_cap, cpu_has_cap);
else
- cpu_die_early();
+ cpu_die_early_with_msg(CAP_CONFLICT_FMT,
+ smp_processor_id(),
caps->capability,
+ caps->desc,
system_has_cap, cpu_has_cap);
+ #undef CAP_CONFLICT_MSG
}
}
@@ -3731,9 +3734,8 @@ __verify_local_elf_hwcaps(const struct
arm64_cpu_capabilities *caps)
for (; caps->matches; caps++)
if (cpus_have_elf_hwcap(caps) && !caps->matches(caps,
SCOPE_LOCAL_CPU)) {
- pr_crit("CPU%d: missing HWCAP: %s\n",
- smp_processor_id(), caps->desc);
- cpu_die_early();
+ cpu_die_early_with_msg("CPU%d: missing HWCAP: %s\n",
+ smp_processor_id(),
caps->desc);
}
}
@@ -3750,9 +3752,8 @@ static void verify_sve_features(void)
unsigned long cpacr = cpacr_save_enable_kernel_sve();
if (vec_verify_vq_map(ARM64_VEC_SVE)) {
- pr_crit("CPU%d: SVE: vector length support mismatch\n",
- smp_processor_id());
- cpu_die_early();
+ cpu_die_early_with_msg("CPU%d: SVE: vector length
support mismatch\n",
+ smp_processor_id());
}
cpacr_restore(cpacr);
@@ -3763,9 +3764,8 @@ static void verify_sme_features(void)
unsigned long cpacr = cpacr_save_enable_kernel_sme();
if (vec_verify_vq_map(ARM64_VEC_SME)) {
- pr_crit("CPU%d: SME: vector length support mismatch\n",
- smp_processor_id());
- cpu_die_early();
+ cpu_die_early_with_msg("CPU%d: SME: vector length
support mismatch\n",
+ smp_processor_id());
}
cpacr_restore(cpacr);
@@ -3776,6 +3776,7 @@ static void verify_hyp_capabilities(void)
u64 safe_mmfr1, mmfr0, mmfr1;
int parange, ipa_max;
unsigned int safe_vmid_bits, vmid_bits;
+ int cpu = smp_processor_id();
if (!IS_ENABLED(CONFIG_KVM))
return;
@@ -3787,19 +3788,15 @@ static void verify_hyp_capabilities(void)
/* Verify VMID bits */
safe_vmid_bits = get_vmid_bits(safe_mmfr1);
vmid_bits = get_vmid_bits(mmfr1);
- if (vmid_bits < safe_vmid_bits) {
- pr_crit("CPU%d: VMID width mismatch\n", smp_processor_id());
- cpu_die_early();
- }
+ if (vmid_bits < safe_vmid_bits)
+ cpu_die_early_with_msg("CPU%d: VMID width mismatch\n", cpu);
/* Verify IPA range */
parange = cpuid_feature_extract_unsigned_field(mmfr0,
ID_AA64MMFR0_EL1_PARANGE_SHIFT);
ipa_max = id_aa64mmfr0_parange_to_phys_shift(parange);
- if (ipa_max < get_kvm_ipa_limit()) {
- pr_crit("CPU%d: IPA range mismatch\n", smp_processor_id());
- cpu_die_early();
- }
+ if (ipa_max < get_kvm_ipa_limit())
+ cpu_die_early_with_msg("CPU%d: IPA range mismatch\n", cpu);
}
static void verify_mpam_capabilities(void)
@@ -3807,29 +3804,24 @@ static void verify_mpam_capabilities(void)
u64 cpu_idr = read_cpuid(ID_AA64PFR0_EL1);
u64 sys_idr = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1);
u16 cpu_partid_max, cpu_pmg_max, sys_partid_max, sys_pmg_max;
+ int cpu = smp_processor_id();
if (FIELD_GET(ID_AA64PFR0_EL1_MPAM_MASK, cpu_idr) !=
- FIELD_GET(ID_AA64PFR0_EL1_MPAM_MASK, sys_idr)) {
- pr_crit("CPU%d: MPAM version mismatch\n",
smp_processor_id());
- cpu_die_early();
- }
+ FIELD_GET(ID_AA64PFR0_EL1_MPAM_MASK, sys_idr))
+ cpu_die_early_with_msg("CPU%d: MPAM version mismatch\n",
cpu);
cpu_idr = read_cpuid(MPAMIDR_EL1);
sys_idr = read_sanitised_ftr_reg(SYS_MPAMIDR_EL1);
if (FIELD_GET(MPAMIDR_EL1_HAS_HCR, cpu_idr) !=
- FIELD_GET(MPAMIDR_EL1_HAS_HCR, sys_idr)) {
- pr_crit("CPU%d: Missing MPAM HCR\n", smp_processor_id());
- cpu_die_early();
- }
+ FIELD_GET(MPAMIDR_EL1_HAS_HCR, sys_idr))
+ cpu_die_early_with_msg("CPU%d: Missing MPAM HCR\n", cpu);
cpu_partid_max = FIELD_GET(MPAMIDR_EL1_PARTID_MAX, cpu_idr);
cpu_pmg_max = FIELD_GET(MPAMIDR_EL1_PMG_MAX, cpu_idr);
sys_partid_max = FIELD_GET(MPAMIDR_EL1_PARTID_MAX, sys_idr);
sys_pmg_max = FIELD_GET(MPAMIDR_EL1_PMG_MAX, sys_idr);
- if (cpu_partid_max < sys_partid_max || cpu_pmg_max < sys_pmg_max) {
- pr_crit("CPU%d: MPAM PARTID/PMG max values are
mismatched\n", smp_processor_id());
- cpu_die_early();
- }
+ if (cpu_partid_max < sys_partid_max || cpu_pmg_max < sys_pmg_max)
+ cpu_die_early_with_msg("CPU%d: MPAM PARTID/PMG max
values are mismatched\n", cpu);
}
/*
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 25dc5afe9ba0..f615b8b79ada 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1057,8 +1057,10 @@ int vec_verify_vq_map(enum vec_type type)
bitmap_complement(tmp_map, tmp_map, SVE_VQ_MAX);
if (bitmap_intersects(tmp_map, info->vq_map, SVE_VQ_MAX)) {
- pr_warn("%s: cpu%d: Required vector length(s) missing\n",
+ #define VEC_MISSING_FMT "%s: cpu%d: Required vector
length(s) missing\n"
+ printk_deferred(KERN_WARNING pr_fmt(VEC_MISSING_FMT),
info->name, smp_processor_id());
+ #undef VEC_MISSING_FMT
return -EINVAL;
}
@@ -1086,8 +1088,10 @@ int vec_verify_vq_map(enum vec_type type)
* no guest is allowed to configure ZCR_EL2.LEN to exceed this:
*/
if (sve_vl_from_vq(__bit_to_vq(b)) <= info->max_virtualisable_vl) {
- pr_warn("%s: cpu%d: Unsupported vector length(s) present\n",
- info->name, smp_processor_id());
+ #define VEC_UNSUPP_FMT "%s: cpu%d: Unsupported vector
length(s) present\n"
+ printk_deferred(KERN_WARNING pr_fmt(VEC_UNSUPP_FMT),
+ info->name, smp_processor_id());
+ #undef VEC_UNSUPP_FMT
return -EINVAL;
}
diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
index 0f4a28b87469..374f34d628ba 100644
--- a/arch/arm64/mm/context.c
+++ b/arch/arm64/mm/context.c
@@ -70,9 +70,8 @@ void verify_cpu_asid_bits(void)
* We cannot decrease the ASID size at runtime, so panic
if we support
* fewer ASID bits than the boot CPU.
*/
- pr_crit("CPU%d: smaller ASID size(%u) than boot CPU (%u)\n",
- smp_processor_id(), asid, asid_bits);
- cpu_panic_kernel();
+ cpu_panic_kernel_with_msg("CPU%d: smaller ASID size(%u)
than boot CPU (%u)\n",
+ smp_processor_id(), asid,
asid_bits);
}
}
>
> Will
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