linux-kernel - Re: [PATCH] s390: fix detection of vector enhancements facility 1 vs. vector packed decimal facility

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Message-ID: <429fab49-91a8-92c5-ec81-71e9336f2571@de.ibm.com>
Date:   Mon, 3 May 2021 14:17:54 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Alexander Egorenkov <egorenar@...ux.ibm.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH] s390: fix detection of vector enhancements facility 1 vs.
 vector packed decimal facility



On 03.05.21 14:12, David Hildenbrand wrote:
> The PoP documents:
> 	134: The vector packed decimal facility is installed in the
> 	     z/Architecture architectural mode. When bit 134 is
> 	     one, bit 129 is also one.
> 	135: The vector enhancements facility 1 is installed in
> 	     the z/Architecture architectural mode. When bit 135
> 	     is one, bit 129 is also one.
> 
> Looks like we confuse the vector enhancements facility 1 ("EXT") with the
> Vector packed decimal facility ("BCD"). Let's fix the facility checks.
> 
> Detected while working on QEMU/tcg z14 support and only unlocking
> the vector enhancements facility 1, but not the vector packed decimal
> facility.
> 
> Fixes: 2583b848cad0 ("s390: report new vector facilities")
> Cc: Heiko Carstens <hca@...ux.ibm.com>
> Cc: Vasily Gorbik <gor@...ux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@...ibm.com>
> Cc: Sven Schnelle <svens@...ux.ibm.com>
> Cc: Alexander Egorenkov <egorenar@...ux.ibm.com>
> Cc: Niklas Schnelle <schnelle@...ux.ibm.com>
> Cc: Janosch Frank <frankja@...ux.ibm.com>
> Cc: linux-s390@...r.kernel.org
> Signed-off-by: David Hildenbrand <david@...hat.com>

Yes looks correct. This should not be noticable on real machines as you either
have both or none, but of course with virtual machine this could happen.

Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>

> ---
>   arch/s390/kernel/setup.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
> index 72134f9f6ff5..5aab59ad5688 100644
> --- a/arch/s390/kernel/setup.c
> +++ b/arch/s390/kernel/setup.c
> @@ -937,9 +937,9 @@ static int __init setup_hwcaps(void)
>   	if (MACHINE_HAS_VX) {
>   		elf_hwcap |= HWCAP_S390_VXRS;
>   		if (test_facility(134))
> -			elf_hwcap |= HWCAP_S390_VXRS_EXT;
> -		if (test_facility(135))
>   			elf_hwcap |= HWCAP_S390_VXRS_BCD;
> +		if (test_facility(135))
> +			elf_hwcap |= HWCAP_S390_VXRS_EXT;
>   		if (test_facility(148))
>   			elf_hwcap |= HWCAP_S390_VXRS_EXT2;
>   		if (test_facility(152))
>