Re: [PATCH v2] KVM: s390: Also reset registers in sync regs for initial cpu reset

[David Hildenbrand <david@redhat.com>]

On 10.03.20 14:12, Christian Borntraeger wrote:
> When we do the initial CPU reset we must not only clear the registers
> in the internal data structures but also in kvm_run sync_regs. For
> modern userspace sync_regs is the only place that it looks at.
> 
> Cc: stable@vger.kernel.org

# v?

> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> ---
>  arch/s390/kvm/kvm-s390.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index d7ff30e45589..c2e6d4ba4e23 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -3268,7 +3268,10 @@ static void kvm_arch_vcpu_ioctl_initial_reset(struct kvm_vcpu *vcpu)
>  	/* Initial reset is a superset of the normal reset */
>  	kvm_arch_vcpu_ioctl_normal_reset(vcpu);
>  
> -	/* this equals initial cpu reset in pop, but we don't switch to ESA */
> +	/*
> +	 * This equals initial cpu reset in pop, but we don't switch to ESA.
> +	 * We do not only reset the internal data, but also ...
> +	 */
>  	vcpu->arch.sie_block->gpsw.mask = 0;
>  	vcpu->arch.sie_block->gpsw.addr = 0;
>  	kvm_s390_set_prefix(vcpu, 0);
> @@ -3278,6 +3281,19 @@ static void kvm_arch_vcpu_ioctl_initial_reset(struct kvm_vcpu *vcpu)
>  	memset(vcpu->arch.sie_block->gcr, 0, sizeof(vcpu->arch.sie_block->gcr));
>  	vcpu->arch.sie_block->gcr[0] = CR0_INITIAL_MASK;
>  	vcpu->arch.sie_block->gcr[14] = CR14_INITIAL_MASK;
> +
> +	/* ... the data in sync regs */
> +	memset(vcpu->run->s.regs.crs, 0, sizeof(vcpu->run->s.regs.crs));
> +	vcpu->run->s.regs.ckc = 0;
> +	vcpu->run->s.regs.crs[0] = CR0_INITIAL_MASK;
> +	vcpu->run->s.regs.crs[14] = CR14_INITIAL_MASK;
> +	vcpu->run->psw_addr = 0;
> +	vcpu->run->psw_mask = 0;
> +	vcpu->run->s.regs.todpr = 0;
> +	vcpu->run->s.regs.cputm = 0;
> +	vcpu->run->s.regs.ckc = 0;
> +	vcpu->run->s.regs.pp = 0;
> +	vcpu->run->s.regs.gbea = 1;
>  	vcpu->run->s.regs.fpc = 0;
>  	vcpu->arch.sie_block->gbea = 1;
>  	vcpu->arch.sie_block->pp = 0;
> 

Acked-by: David Hildenbrand <david@redhat.com>

However, I do wonder if that ioctl *originally* was designed for that -
IOW if this is rally a stable patch or just some change that makes
sense. IIRC, userspace/QEMU always did the right thing, no? There was no
documentation about the guarantees AFAIK.

-- 
Thanks,

David / dhildenb