Re: [PATCH 3/3] s390/uvdevice: autoload module based on CPU facility

[Steffen Eiden <seiden@xxxxxxxxxxxxx>]

On 7/12/22 18:49, Claudio Imbrenda wrote:
> On Tue, 12 Jul 2022 12:52:20 +0200
> Steffen Eiden <seiden@xxxxxxxxxxxxx> wrote:
>
> > Make sure the uvdevice driver will be automatically loaded when
> > facility 158 is available.
> >
> > Signed-off-by: Steffen Eiden <seiden@xxxxxxxxxxxxx>
> > ---
> >   arch/s390/include/asm/cpufeature.h | 1 +
> >   arch/s390/kernel/cpufeature.c      | 1 +
> >   drivers/s390/char/uvdevice.c       | 5 ++---
> >   3 files changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/s390/include/asm/cpufeature.h b/arch/s390/include/asm/cpufeature.h
> > index aa8081dad411..4b17f876ab54 100644
> > --- a/arch/s390/include/asm/cpufeature.h
> > +++ b/arch/s390/include/asm/cpufeature.h
> > @@ -33,6 +33,7 @@ enum {
> >   	S390_CPU_FEATURE_NNPA,
> >   	S390_CPU_FEATURE_PCI_MIO,
> >   	S390_CPU_FEATURE_SIE,
> > +	S390_CPU_FEATURE_UV,
> >   	MAX_CPU_FEATURES
> >   };
> >   
> > diff --git a/arch/s390/kernel/cpufeature.c b/arch/s390/kernel/cpufeature.c
> > index e70b29804db4..0b854d37edcb 100644
> > --- a/arch/s390/kernel/cpufeature.c
> > +++ b/arch/s390/kernel/cpufeature.c
> > @@ -42,6 +42,7 @@ static struct s390_cpu_feature s390_cpu_features[MAX_CPU_FEATURES] = {
> >   	[S390_CPU_FEATURE_NNPA]		= {.type = TYPE_HWCAP, .num = HWCAP_NR_NNPA},
> >   	[S390_CPU_FEATURE_PCI_MIO]	= {.type = TYPE_HWCAP, .num = HWCAP_NR_PCI_MIO},
> >   	[S390_CPU_FEATURE_SIE]		= {.type = TYPE_HWCAP, .num = HWCAP_NR_SIE},
> > +	[S390_CPU_FEATURE_UV]		= {.type = TYPE_FACILITY, .num = 158},
> >   };
> >   
> >   /*
> > diff --git a/drivers/s390/char/uvdevice.c b/drivers/s390/char/uvdevice.c
> > index 66505d7166a6..1d40457c7b10 100644
> > --- a/drivers/s390/char/uvdevice.c
> > +++ b/drivers/s390/char/uvdevice.c
> > @@ -27,6 +27,7 @@
> >   #include <linux/stddef.h>
> >   #include <linux/vmalloc.h>
> >   #include <linux/slab.h>
> > +#include <linux/cpufeature.h>
> >   
> >   #include <asm/uvdevice.h>
> >   #include <asm/uv.h>
> > @@ -244,12 +245,10 @@ static void __exit uvio_dev_exit(void)
> >   
> >   static int __init uvio_dev_init(void)
> >   {
> > -	if (!test_facility(158))
> > -		return -ENXIO;
> >   	return misc_register(&uvio_dev_miscdev);
> >   }
> >   
> > -module_init(uvio_dev_init);
> > +module_cpu_feature_match(S390_CPU_FEATURE_UV, uvio_dev_init);
>
> does this still prevent manual loading when the feature is not present?
yes.

Have a look at the macro definition at 'include/linux/cpufeature.h':

Use module_cpu_feature_match(feature, module_init_function) to 

declare that 

[snip]
b) the module must not be loaded if CPU feature 'feature' is not present 

   (not even by manual insmod).

The test 'facility(158)' just moved to cpu_have_feature() in 
'/arch/s390/kernel/cpufeature.c'.
> >   module_exit(uvio_dev_exit);
> >   
> >   MODULE_AUTHOR("IBM Corporation");