[PATCH v2 08/23] arm64: cpufeature: Store every ID register with its overrides applied
Ben Horgan
ben.horgan at arm.com
Fri Oct 9 08:51:14 PDT 2026
Hi Will,
On 10/9/26 11:07, Will Deacon wrote:
> From: Fuad Tabba <fuad.tabba at linux.dev>
>
> __cpuinfo_store_cpu() stores ID_AA64PFR0_EL1 and ID_AA64PFR1_EL1 with
> their overrides applied and every other register raw. Store the rest
> the same way. Everything read with read_cpuid() goes through
> read_cpuid_with_overrides(). CTR_EL0 and CNTFRQ_EL0, which are read
> otherwise, go through arm64_ftr_reg_override(). It returns a register
> with no override unchanged, so an override added to one later takes
> effect without a change here.
>
> init_cpu_ftr_reg() then gets values that already carry every valid
> override, so its code to apply one is dead. Remove that code.
> init_cpu_ftr_reg() still removes an unsafe override, so the same
> overrides are rejected and sys_val is unchanged. Only its log changes.
> The raw value is gone, so it logs an override equal to that value as
> "forced" rather than "already set".
>
> Secondaries are compared with the boot CPU on their stored values, so
> CPUs that differ only in a field the command line turned off no longer
> taint the kernel.
>
> Suggested-by: Will Deacon <will at kernel.org>
> Signed-off-by: Fuad Tabba <fuad.tabba at linux.dev>
> Signed-off-by: Will Deacon <will at kernel.org>
> ---
> arch/arm64/kernel/cpufeature.c | 17 +++----
> arch/arm64/kernel/cpuinfo.c | 82 +++++++++++++++++-----------------
> 2 files changed, 46 insertions(+), 53 deletions(-)
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 9212f10c1d1a..d69a5b8304b6 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1043,6 +1043,8 @@ void __init validate_ftr_regs(void)
> * Also initialises the strict_mask for the register.
> * Any bits that are not covered by an arm64_ftr_bits entry are considered
> * RES0 for the system-wide value, and must strictly match.
> + * @new has been through arm64_ftr_reg_override(), so a valid override is
> + * already applied to it. Only an unsafe one is left to remove here.
> */
> static void init_cpu_ftr_reg(u32 sys_reg, u64 new)
> {
> @@ -1063,29 +1065,20 @@ static void init_cpu_ftr_reg(u32 sys_reg, u64 new)
> s64 ftr_ovr = arm64_ftr_value(ftrp, reg->override->val);
>
> if ((ftr_mask & reg->override->mask) == ftr_mask) {
> - s64 tmp = arm64_ftr_safe_value(ftrp, ftr_ovr, ftr_new);
> - char *str = NULL;
> + char *str = "forced";
>
> - if (ftr_ovr != tmp) {
> + if (arm64_ftr_safe_value(ftrp, ftr_ovr, ftr_new) != ftr_ovr) {
> /* Unsafe, remove the override */
> reg->override->mask &= ~ftr_mask;
> reg->override->val &= ~ftr_mask;
> - tmp = ftr_ovr;
> str = "ignoring override";
> - } else if (ftr_new != tmp) {
> - /* Override was valid */
> - ftr_new = tmp;
> - str = "forced";
> - } else {
> - /* Override was the safe value */
> - str = "already set";
> }
>
> pr_warn("%s[%d:%d]: %s to %llx\n",
> reg->name,
> ftrp->shift + ftrp->width - 1,
> ftrp->shift, str,
> - tmp & (BIT(ftrp->width) - 1));
> + ftr_ovr & (BIT(ftrp->width) - 1));
> } else if ((ftr_mask & reg->override->val) == ftr_mask) {
> reg->override->val &= ~ftr_mask;
> pr_warn("%s[%d:%d]: impossible override, ignored\n",
> diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
> index 0ae40b0c7b2f..1b92e52989b1 100644
> --- a/arch/arm64/kernel/cpuinfo.c
> +++ b/arch/arm64/kernel/cpuinfo.c
> @@ -443,33 +443,33 @@ static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info)
>
> static void __cpuinfo_store_cpu_32bit(struct cpuinfo_32bit *info)
> {
> - info->reg_id_dfr0 = read_cpuid(ID_DFR0_EL1);
> - info->reg_id_dfr1 = read_cpuid(ID_DFR1_EL1);
> - info->reg_id_isar0 = read_cpuid(ID_ISAR0_EL1);
> - info->reg_id_isar1 = read_cpuid(ID_ISAR1_EL1);
> - info->reg_id_isar2 = read_cpuid(ID_ISAR2_EL1);
> - info->reg_id_isar3 = read_cpuid(ID_ISAR3_EL1);
> - info->reg_id_isar4 = read_cpuid(ID_ISAR4_EL1);
> - info->reg_id_isar5 = read_cpuid(ID_ISAR5_EL1);
> - info->reg_id_isar6 = read_cpuid(ID_ISAR6_EL1);
> - info->reg_id_mmfr0 = read_cpuid(ID_MMFR0_EL1);
> - info->reg_id_mmfr1 = read_cpuid(ID_MMFR1_EL1);
> - info->reg_id_mmfr2 = read_cpuid(ID_MMFR2_EL1);
> - info->reg_id_mmfr3 = read_cpuid(ID_MMFR3_EL1);
> - info->reg_id_mmfr4 = read_cpuid(ID_MMFR4_EL1);
> - info->reg_id_mmfr5 = read_cpuid(ID_MMFR5_EL1);
> - info->reg_id_pfr0 = read_cpuid(ID_PFR0_EL1);
> - info->reg_id_pfr1 = read_cpuid(ID_PFR1_EL1);
> - info->reg_id_pfr2 = read_cpuid(ID_PFR2_EL1);
> + info->reg_id_dfr0 = read_cpuid_with_overrides(ID_DFR0_EL1);
> + info->reg_id_dfr1 = read_cpuid_with_overrides(ID_DFR1_EL1);
> + info->reg_id_isar0 = read_cpuid_with_overrides(ID_ISAR0_EL1);
> + info->reg_id_isar1 = read_cpuid_with_overrides(ID_ISAR1_EL1);
> + info->reg_id_isar2 = read_cpuid_with_overrides(ID_ISAR2_EL1);
> + info->reg_id_isar3 = read_cpuid_with_overrides(ID_ISAR3_EL1);
> + info->reg_id_isar4 = read_cpuid_with_overrides(ID_ISAR4_EL1);
> + info->reg_id_isar5 = read_cpuid_with_overrides(ID_ISAR5_EL1);
> + info->reg_id_isar6 = read_cpuid_with_overrides(ID_ISAR6_EL1);
> + info->reg_id_mmfr0 = read_cpuid_with_overrides(ID_MMFR0_EL1);
> + info->reg_id_mmfr1 = read_cpuid_with_overrides(ID_MMFR1_EL1);
> + info->reg_id_mmfr2 = read_cpuid_with_overrides(ID_MMFR2_EL1);
> + info->reg_id_mmfr3 = read_cpuid_with_overrides(ID_MMFR3_EL1);
> + info->reg_id_mmfr4 = read_cpuid_with_overrides(ID_MMFR4_EL1);
> + info->reg_id_mmfr5 = read_cpuid_with_overrides(ID_MMFR5_EL1);
> + info->reg_id_pfr0 = read_cpuid_with_overrides(ID_PFR0_EL1);
> + info->reg_id_pfr1 = read_cpuid_with_overrides(ID_PFR1_EL1);
> + info->reg_id_pfr2 = read_cpuid_with_overrides(ID_PFR2_EL1);
>
> - info->reg_mvfr0 = read_cpuid(MVFR0_EL1);
> - info->reg_mvfr1 = read_cpuid(MVFR1_EL1);
> - info->reg_mvfr2 = read_cpuid(MVFR2_EL1);
> + info->reg_mvfr0 = read_cpuid_with_overrides(MVFR0_EL1);
> + info->reg_mvfr1 = read_cpuid_with_overrides(MVFR1_EL1);
> + info->reg_mvfr2 = read_cpuid_with_overrides(MVFR2_EL1);
> }
>
> static void __cpuinfo_store_cpu(struct cpuinfo_arm64 *info)
> {
> - info->reg_cntfrq = arch_timer_get_cntfrq();
> + info->reg_cntfrq = arm64_ftr_reg_override(SYS_CNTFRQ_EL0, arch_timer_get_cntfrq());
> /*
> * Use the effective value of the CTR_EL0 than the raw value
> * exposed by the CPU. CTR_EL0.IDC field value must be interpreted
> @@ -478,35 +478,35 @@ static void __cpuinfo_store_cpu(struct cpuinfo_arm64 *info)
> * effective value of the CTR_EL0 in our internal records for
> * accurate sanity check and feature enablement.
> */
> - info->reg_ctr = read_cpuid_effective_cachetype();
> - info->reg_dczid = read_cpuid(DCZID_EL0);
> + info->reg_ctr = arm64_ftr_reg_override(SYS_CTR_EL0, read_cpuid_effective_cachetype());
> + info->reg_dczid = read_cpuid_with_overrides(DCZID_EL0);
> info->reg_midr = read_cpuid_id();
> info->reg_revidr = read_cpuid(REVIDR_EL1);
> info->reg_aidr = read_cpuid(AIDR_EL1);
>
> - info->reg_id_aa64dfr0 = read_cpuid(ID_AA64DFR0_EL1);
> - info->reg_id_aa64dfr1 = read_cpuid(ID_AA64DFR1_EL1);
> - info->reg_id_aa64isar0 = read_cpuid(ID_AA64ISAR0_EL1);
> - info->reg_id_aa64isar1 = read_cpuid(ID_AA64ISAR1_EL1);
> - info->reg_id_aa64isar2 = read_cpuid(ID_AA64ISAR2_EL1);
> - info->reg_id_aa64isar3 = read_cpuid(ID_AA64ISAR3_EL1);
> - info->reg_id_aa64mmfr0 = read_cpuid(ID_AA64MMFR0_EL1);
> - info->reg_id_aa64mmfr1 = read_cpuid(ID_AA64MMFR1_EL1);
> - info->reg_id_aa64mmfr2 = read_cpuid(ID_AA64MMFR2_EL1);
> - info->reg_id_aa64mmfr3 = read_cpuid(ID_AA64MMFR3_EL1);
> - info->reg_id_aa64mmfr4 = read_cpuid(ID_AA64MMFR4_EL1);
> + info->reg_id_aa64dfr0 = read_cpuid_with_overrides(ID_AA64DFR0_EL1);
> + info->reg_id_aa64dfr1 = read_cpuid_with_overrides(ID_AA64DFR1_EL1);
> + info->reg_id_aa64isar0 = read_cpuid_with_overrides(ID_AA64ISAR0_EL1);
> + info->reg_id_aa64isar1 = read_cpuid_with_overrides(ID_AA64ISAR1_EL1);
> + info->reg_id_aa64isar2 = read_cpuid_with_overrides(ID_AA64ISAR2_EL1);
> + info->reg_id_aa64isar3 = read_cpuid_with_overrides(ID_AA64ISAR3_EL1);
> + info->reg_id_aa64mmfr0 = read_cpuid_with_overrides(ID_AA64MMFR0_EL1);
> + info->reg_id_aa64mmfr1 = read_cpuid_with_overrides(ID_AA64MMFR1_EL1);
> + info->reg_id_aa64mmfr2 = read_cpuid_with_overrides(ID_AA64MMFR2_EL1);
> + info->reg_id_aa64mmfr3 = read_cpuid_with_overrides(ID_AA64MMFR3_EL1);
> + info->reg_id_aa64mmfr4 = read_cpuid_with_overrides(ID_AA64MMFR4_EL1);
> info->reg_id_aa64pfr0 = read_cpuid_with_overrides(ID_AA64PFR0_EL1);
> info->reg_id_aa64pfr1 = read_cpuid_with_overrides(ID_AA64PFR1_EL1);
> - info->reg_id_aa64pfr2 = read_cpuid(ID_AA64PFR2_EL1);
> - info->reg_id_aa64zfr0 = read_cpuid(ID_AA64ZFR0_EL1);
> - info->reg_id_aa64smfr0 = read_cpuid(ID_AA64SMFR0_EL1);
> - info->reg_id_aa64fpfr0 = read_cpuid(ID_AA64FPFR0_EL1);
> + info->reg_id_aa64pfr2 = read_cpuid_with_overrides(ID_AA64PFR2_EL1);
> + info->reg_id_aa64zfr0 = read_cpuid_with_overrides(ID_AA64ZFR0_EL1);
> + info->reg_id_aa64smfr0 = read_cpuid_with_overrides(ID_AA64SMFR0_EL1);
> + info->reg_id_aa64fpfr0 = read_cpuid_with_overrides(ID_AA64FPFR0_EL1);
>
> if (IS_ENABLED(CONFIG_ARM64_MTE) && id_aa64pfr1_mte(info->reg_id_aa64pfr1))
> - info->reg_gmid = read_cpuid(GMID_EL1);
> + info->reg_gmid = read_cpuid_with_overrides(GMID_EL1);
>
> if (id_aa64pfr0_mpam(info->reg_id_aa64pfr0) || id_aa64pfr1_mpamfrac(info->reg_id_aa64pfr1))
> - info->reg_mpamidr = read_cpuid(MPAMIDR_EL1);
> + info->reg_mpamidr = read_cpuid_with_overrides(MPAMIDR_EL1);
>
> if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0))
> __cpuinfo_store_cpu_32bit(&info->aarch32);
For completeness shouldn't read_cpuid(SMIDR_EL1) change to
read_cpuid_with_overrides(SMIDR_EL1)?
Thanks,
Ben
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