Re: [PATCH 1/2] KVM: s390: Fix lpsw/e breaking event handling

[Heiko Carstens <hca@linux.ibm.com>]

On Mon, Mar 23, 2026 at 03:35:22PM +0000, Janosch Frank wrote:
> LPSW and LPSWE need to set the gbea on completion but currently don't.
> Time to fix this up.
> 
> LPSWEY was designed to not set the bear.
> 
> Fixes: 48a3e950f4cee ("KVM: s390: Add support for machine checks.")
> Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
>  arch/s390/kvm/priv.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index a3250ad83a8e..cc0553da14cb 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -714,12 +714,13 @@ int kvm_s390_handle_lpsw(struct kvm_vcpu *vcpu)
>  {
>  	psw_t *gpsw = &vcpu->arch.sie_block->gpsw;
>  	psw32_t new_psw;
> -	u64 addr;
> +	u64 addr, iaddr;
>  	int rc;
>  	u8 ar;
>  
>  	vcpu->stat.instruction_lpsw++;
>  
> +	iaddr = gpsw->addr - kvm_s390_get_ilen(vcpu);
>  	if (gpsw->mask & PSW_MASK_PSTATE)
>  		return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
>  
> @@ -737,18 +738,20 @@ int kvm_s390_handle_lpsw(struct kvm_vcpu *vcpu)
>  	gpsw->addr = new_psw.addr & ~PSW32_ADDR_AMODE;
>  	if (!is_valid_psw(gpsw))
>  		return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
> +	vcpu->arch.sie_block->gbea = iaddr;
>  	return 0;

This doesn't look correct to me: even if there is an early specification
exception the PSW is still replaced, and hence the breaking event address
needs to be updated. Read: the gbea assignment should be moved before
the is_valid_psw() check.

>  static int handle_lpswe(struct kvm_vcpu *vcpu)
>  {
>  	psw_t new_psw;
> -	u64 addr;
> +	u64 addr, iaddr;
>  	int rc;

This breaks reverse x-mas style. :)

> @@ -761,6 +764,7 @@ static int handle_lpswe(struct kvm_vcpu *vcpu)
>  	vcpu->arch.sie_block->gpsw = new_psw;
>  	if (!is_valid_psw(&vcpu->arch.sie_block->gpsw))
>  		return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
> +	vcpu->arch.sie_block->gbea = iaddr;
>  	return 0;

Like above, I believe this is not correct.