Re: [PATCH] arm64: Add the arm64.nolse_atomics command line option

Aiqun(Maria) Yu
2023-07-10T08:20:42Z

On 7/10/2023 3:27 PM, Marc Zyngier wrote:
> On Mon, 10 Jul 2023 06:59:55 +0100,
> Maria Yu <quic_aiquny@quicinc.com> wrote:
>>
>> In order to be able to disable lse_atomic even if cpu
>> support it, most likely because of memory controller
>> cannot deal with the lse atomic instructions, use a
>> new idreg override to deal with it.
>
> In general, the idreg overrides are *not* there to paper over HW bugs.
> They are there to force the kernel to use or disable a feature for
> performance reason or to guide the *enabling* of a feature, but not
> because the HW is broken.
>
> The broken status of a HW platform must also be documented so that we
> know what to expect when we look at, for example, a bad case of memory
> corruption (something I'd expect to see on a system that only
> partially implements atomic memory operations).
>

good idea. A noc error would be happened if the lse atomic instruction
happened during a memory controller doesn't support lse atomic instructions.
I can put the information in next patchset comment message. Pls feel
free to let know if there is other place to have this kind of
information with.
>>
>> Signed-off-by: Maria Yu <quic_aiquny@quicinc.com>
>> ---
>> Documentation/admin-guide/kernel-parameters.txt | 2 ++
>> arch/arm64/include/asm/cpufeature.h | 1 +
>> arch/arm64/kernel/cpufeature.c | 4 +++-
>> arch/arm64/kernel/idreg-override.c | 11 +++++++++++
>> 4 files changed, 17 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 85fb0fa5d091..6ad754549f1d 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -433,6 +433,8 @@
>> arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory
>> Set instructions support
>>
>> + arm64.nolse_atomic [ARM64] Unconditionally disable LSE Atomic support
>> +
>
> 'nolse', or 'noatomic' should be enough. In general, the suffix should
> be either derived from the FEAT_* name or the idreg field name.

noatomic can be used in next patchset.
ID_AA64ISAR0_EL1_ATOMIC_SHIFT
>
>> ataflop= [HW,M68k]
>>
>> atarimouse= [HW,MOUSE] Atari Mouse
>> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
>> index 96e50227f940..9d56dea1fe62 100644
>> --- a/arch/arm64/include/asm/cpufeature.h
>> +++ b/arch/arm64/include/asm/cpufeature.h
>> @@ -916,6 +916,7 @@ extern struct arm64_ftr_override id_aa64pfr0_override;
>> extern struct arm64_ftr_override id_aa64pfr1_override;
>> extern struct arm64_ftr_override id_aa64zfr0_override;
>> extern struct arm64_ftr_override id_aa64smfr0_override;
>> +extern struct arm64_ftr_override id_aa64isar0_override;
>> extern struct arm64_ftr_override id_aa64isar1_override;
>> extern struct arm64_ftr_override id_aa64isar2_override;
>>
>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>> index f9d456fe132d..9bd766880807 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -669,6 +669,7 @@ struct arm64_ftr_override __ro_after_init id_aa64pfr0_override;
>> struct arm64_ftr_override __ro_after_init id_aa64pfr1_override;
>> struct arm64_ftr_override __ro_after_init id_aa64zfr0_override;
>> struct arm64_ftr_override __ro_after_init id_aa64smfr0_override;
>> +struct arm64_ftr_override __ro_after_init id_aa64isar0_override;
>> struct arm64_ftr_override __ro_after_init id_aa64isar1_override;
>> struct arm64_ftr_override __ro_after_init id_aa64isar2_override;
>>
>> @@ -721,7 +722,8 @@ static const struct __ftr_reg_entry {
>> ARM64_FTR_REG(SYS_ID_AA64DFR1_EL1, ftr_raz),
>>
>> /* Op1 = 0, CRn = 0, CRm = 6 */
>> - ARM64_FTR_REG(SYS_ID_AA64ISAR0_EL1, ftr_id_aa64isar0),
>> + ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64ISAR0_EL1, ftr_id_aa64isar0,
>> + &id_aa64isar0_override),
>> ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64ISAR1_EL1, ftr_id_aa64isar1,
>> &id_aa64isar1_override),
>> ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64ISAR2_EL1, ftr_id_aa64isar2,
>> diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
>> index 2fe2491b692c..af41ab4f3d94 100644
>> --- a/arch/arm64/kernel/idreg-override.c
>> +++ b/arch/arm64/kernel/idreg-override.c
>> @@ -105,6 +105,15 @@ static const struct ftr_set_desc pfr1 __initconst = {
>> },
>> };
>>
>> +static const struct ftr_set_desc isar0 __initconst = {
>> + .name = "id_aa64isar0",
>> + .override = &id_aa64isar0_override,
>> + .fields = {
>> + FIELD("atomic", ID_AA64ISAR0_EL1_ATOMIC_SHIFT, NULL),
>> + {}
>> + },
>> +};
>> +
>> static const struct ftr_set_desc isar1 __initconst = {
>> .name = "id_aa64isar1",
>> .override = &id_aa64isar1_override,
>> @@ -163,6 +172,7 @@ static const struct ftr_set_desc * const regs[] __initconst = {
>> &mmfr1,
>> &pfr0,
>> &pfr1,
>> + &isar0,
>> &isar1,
>> &isar2,
>> &smfr0,
>> @@ -185,6 +195,7 @@ static const struct {
>> { "arm64.nomops", "id_aa64isar2.mops=0" },
>> { "arm64.nomte", "id_aa64pfr1.mte=0" },
>> { "nokaslr", "arm64_sw.nokaslr=1" },
>> + { "arm64.nolse_atomic", "id_aa64isar0.atomic=0" },
>
> And what of 32bit?
>
> M.