Re: [RFC PATCH v2 4/4] arm64: Export id_aar64fpr0 via sysfs

[Qais Yousef <qais.yousef@arm.com>]

On 10/21/20 13:28, Greg Kroah-Hartman wrote:
> On Wed, Oct 21, 2020 at 11:46:11AM +0100, Qais Yousef wrote:
> > So that userspace can detect if the cpu has aarch32 support at EL0.
> > 
> > CPUREGS_ATTR_RO() was renamed to CPUREGS_RAW_ATTR_RO() to better reflect
> > what it does. And fixed to accept both u64 and u32 without causing the
> > printf to print out a warning about mismatched type. This was caught
> > while testing to check the new CPUREGS_USER_ATTR_RO().
> > 
> > The new CPUREGS_USER_ATTR_RO() exports a Sanitised or RAW sys_reg based
> > on a @cond to user space. The exported fields match the definition in
> > arm64_ftr_reg so that the content of a register exported via MRS and
> > sysfs are kept cohesive.
> > 
> > The @cond in our case is that the system is asymmetric aarch32 and the
> > controlling sysctl.enable_asym_32bit is enabled.
> > 
> > Update Documentation/arm64/cpu-feature-registers.rst to reflect the
> > newly visible EL0 field in ID_AA64FPR0_EL1.
> > 
> > Note that the MRS interface will still return the sanitized content
> > _only_.
> > 
> > Signed-off-by: Qais Yousef <qais.yousef@arm.com>
> > ---
> > 
> > Example output. I was surprised that the 2nd field (bits[7:4]) is printed out
> > although it's set as FTR_HIDDEN.
> > 
> > # cat /sys/devices/system/cpu/cpu*/regs/identification/id_aa64pfr0
> > 0x0000000000000011
> > 0x0000000000000011
> > 0x0000000000000011
> > 0x0000000000000011
> > 0x0000000000000011
> > 0x0000000000000011
> > 
> > # echo 1 > /proc/sys/kernel/enable_asym_32bit
> > 
> > # cat /sys/devices/system/cpu/cpu*/regs/identification/id_aa64pfr0
> > 0x0000000000000011
> > 0x0000000000000011
> > 0x0000000000000012
> > 0x0000000000000012
> > 0x0000000000000011
> > 0x0000000000000011
> > 
> >  Documentation/arm64/cpu-feature-registers.rst |  2 +-
> >  arch/arm64/kernel/cpufeature.c                |  2 +-
> >  arch/arm64/kernel/cpuinfo.c                   | 58 +++++++++++++++++--
> >  3 files changed, 54 insertions(+), 8 deletions(-)
> > 
> > diff --git a/Documentation/arm64/cpu-feature-registers.rst b/Documentation/arm64/cpu-feature-registers.rst
> > index f28853f80089..bfcbda6d6f35 100644
> > --- a/Documentation/arm64/cpu-feature-registers.rst
> > +++ b/Documentation/arm64/cpu-feature-registers.rst
> > @@ -166,7 +166,7 @@ infrastructure:
> >       +------------------------------+---------+---------+
> >       | EL1                          | [7-4]   |    n    |
> >       +------------------------------+---------+---------+
> > -     | EL0                          | [3-0]   |    n    |
> > +     | EL0                          | [3-0]   |    y    |
> >       +------------------------------+---------+---------+
> >  
> >  
> > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > index 6f795c8221f4..0f7307c8ad80 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -221,7 +221,7 @@ static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
> >  	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL3_SHIFT, 4, 0),
> >  	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL2_SHIFT, 4, 0),
> >  	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL1_SHIFT, 4, ID_AA64PFR0_EL1_64BIT_ONLY),
> > -	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL0_SHIFT, 4, ID_AA64PFR0_EL0_64BIT_ONLY),
> > +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_EL0_SHIFT, 4, ID_AA64PFR0_EL0_64BIT_ONLY),
> >  	ARM64_FTR_END,
> >  };
> >  
> > diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
> > index 93c55986ca7f..632b9d5b5230 100644
> > --- a/arch/arm64/kernel/cpuinfo.c
> > +++ b/arch/arm64/kernel/cpuinfo.c
> > @@ -231,25 +231,71 @@ static struct kobj_type cpuregs_kobj_type = {
> >   * future expansion without an ABI break.
> >   */
> >  #define kobj_to_cpuinfo(kobj)	container_of(kobj, struct cpuinfo_arm64, kobj)
> > -#define CPUREGS_ATTR_RO(_name, _field)						\
> > +#define CPUREGS_RAW_ATTR_RO(_name, _field)				\
> >  	static ssize_t _name##_show(struct kobject *kobj,			\
> >  			struct kobj_attribute *attr, char *buf)			\
> >  	{									\
> >  		struct cpuinfo_arm64 *info = kobj_to_cpuinfo(kobj);		\
> >  										\
> > -		if (info->reg_midr)						\
> > -			return sprintf(buf, "0x%016x\n", info->reg_##_field);	\
> > -		else								\
> > +		if (info->reg_midr) {						\
> > +			u64 val = info->reg_##_field;				\
> > +			return sprintf(buf, "0x%016llx\n", val);		\
> 
> Nit, for sysfs, use the new sysfs_emit() call instead of sprintf().

Will do.

Thanks!

--
Qais Yousef