linux-kernel - Re: [PATCH v1] KVM: s390: store DXC/VXC in fpc on DATA/Vector-processing exceptions

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Date:   Wed, 22 Aug 2018 12:31:51 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-s390@...r.kernel.org,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
Subject: Re: [PATCH v1] KVM: s390: store DXC/VXC in fpc on
 DATA/Vector-processing exceptions

On 22.08.2018 11:53, David Hildenbrand wrote:
> When DATA exceptions and vector-processing exceptions (program interrupts)
> are injected, the DXC/VXC is also to be stored in the fpc, if AFP is
> enabled in CR0.
> 
> This can happen inside KVM when reinjecting an interrupt during program
> interrupt intercepts. These are triggered for example when debugging the
> guest (concurrent PER events result in an intercept instead of an
> injection of such interrupts).
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
> 
> Only compile-tested.

It baffles me that AFP is still a thing in zArch mode. I would have
expected it to be a default 1. But then again, I just found out about it.

POP checks out:
Reviewed-by: Janosch Frank <frankja@...ux.ibm.com>


> 
>  arch/s390/include/asm/ctl_reg.h | 1 +
>  arch/s390/kvm/interrupt.c       | 8 ++++++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/arch/s390/include/asm/ctl_reg.h b/arch/s390/include/asm/ctl_reg.h
> index 4600453536c2..88f3f14baee9 100644
> --- a/arch/s390/include/asm/ctl_reg.h
> +++ b/arch/s390/include/asm/ctl_reg.h
> @@ -11,6 +11,7 @@
>  #include <linux/const.h>
>  
>  #define CR0_CLOCK_COMPARATOR_SIGN	_BITUL(63 - 10)
> +#define CR0_AFP_REGISTER_CONTROL	_BITUL(63 - 45)
>  #define CR0_EMERGENCY_SIGNAL_SUBMASK	_BITUL(63 - 49)
>  #define CR0_EXTERNAL_CALL_SUBMASK	_BITUL(63 - 50)
>  #define CR0_CLOCK_COMPARATOR_SUBMASK	_BITUL(63 - 52)
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index fcb55b02990e..5b5754d8f460 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -765,6 +765,14 @@ static int __must_check __deliver_prog(struct kvm_vcpu *vcpu)
>  		break;
>  	case PGM_VECTOR_PROCESSING:
>  	case PGM_DATA:
> +		if (vcpu->arch.sie_block->gcr[0] & CR0_AFP_REGISTER_CONTROL) {
> +			/* make sure the new fpc will be lazily loaded */
> +			save_fpu_regs();
> +			/* the DXC/VXC cannot make the fpc invalid */
> +			current->thread.fpu.fpc &= ~0xff00u;
> +			current->thread.fpu.fpc |= (pgm_info.data_exc_code << 8)
> +						   & 0xff00u;

Everything except that byte should be 0 anyway when it comes from
lowcore, why do you mask?

> +		}
>  		rc = put_guest_lc(vcpu, pgm_info.data_exc_code,
>  				  (u32 *)__LC_DATA_EXC_CODE);
>  		break;
> 




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