linux-kernel - Re: [PATCH 4.4 15/50] s390/alternative: use a copy of the facility bit mask

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Date:   Fri, 4 May 2018 09:37:20 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>
Subject: Re: [PATCH 4.4 15/50] s390/alternative: use a copy of the facility
 bit mask

On 04/27/2018, 03:58 PM, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Martin Schwidefsky <schwidefsky@...ibm.com>
> 
> 
> [ Upstream commit cf1489984641369611556bf00c48f945c77bcf02 ]
> 
> To be able to switch off specific CPU alternatives with kernel parameters
> make a copy of the facility bit mask provided by STFLE and use the copy
> for the decision to apply an alternative.
...
> --- a/arch/s390/include/asm/facility.h
> +++ b/arch/s390/include/asm/facility.h
> @@ -13,6 +13,24 @@
>  
>  #define MAX_FACILITY_BIT (256*8)	/* stfle_fac_list has 256 bytes */

I wonder if the below (plus __test_facility) is correct in 4.4, given
MAX_FACILITY_BIT is defined as such and not as sizeof(stfle_fac_list *
8) as in upstream?

> +static inline void __set_facility(unsigned long nr, void *facilities)
> +{
> +	unsigned char *ptr = (unsigned char *) facilities;
> +
> +	if (nr >= MAX_FACILITY_BIT)
> +		return;
> +	ptr[nr >> 3] |= 0x80 >> (nr & 7);
> +}
> +
> +static inline void __clear_facility(unsigned long nr, void *facilities)
> +{
> +	unsigned char *ptr = (unsigned char *) facilities;
> +
> +	if (nr >= MAX_FACILITY_BIT)
> +		return;
> +	ptr[nr >> 3] &= ~(0x80 >> (nr & 7));
> +}
> +
>  static inline int __test_facility(unsigned long nr, void *facilities)
>  {
>  	unsigned char *ptr;
> --- a/arch/s390/include/asm/lowcore.h
> +++ b/arch/s390/include/asm/lowcore.h
> @@ -170,7 +170,8 @@ struct _lowcore {
>  	__u8	pad_0x0e20[0x0f00-0x0e20];	/* 0x0e20 */
>  
>  	/* Extended facility list */
> -	__u64	stfle_fac_list[32];		/* 0x0f00 */
> +	__u64	stfle_fac_list[16];		/* 0x0f00 */
> +	__u64	alt_stfle_fac_list[16];		/* 0x0f80 */
>  	__u8	pad_0x1000[0x11b0-0x1000];	/* 0x1000 */

thanks,
-- 
js
suse labs