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

Janosch Frank
2018-08-22T10:31:51Z

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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@redhat.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@linux.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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