Re: [PATCH] KVM: s390: Don't WARN on PV validities

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Thu,  6 Jul 2023 14:53:35 +0000
Janosch Frank <frankja@linux.ibm.com> wrote:

> Validities usually indicate KVM errors and as such we want to print a
> message with a high priority to alert users that a validity
> occurred. With the introduction of Protected VMs it's become very easy
> to trigger validities via IOCTLs if the VM is in PV mode.
> 
> An optimal solution would be to return EINVALs to all IOCTLs that
> could result in such a situation. Unfortunately there are quite a lot
> of ways to trigger PV validities since the number of allowed SCB data
> combinations are very limited by FW in order to provide the guest's
> security.
> 
> Let's only log those validities to the KVM sysfs log and skip the
> WARN_ONCE(). This way we get a longish lasting log entry.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
> 
> int -> ext:
>  * Fixed range
>  * Extended commit message 
> 
> ---
>  arch/s390/kvm/intercept.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
> index 954d39adf85c..f3c1220fd1e2 100644
> --- a/arch/s390/kvm/intercept.c
> +++ b/arch/s390/kvm/intercept.c
> @@ -97,9 +97,15 @@ static int handle_validity(struct kvm_vcpu *vcpu)
>  	KVM_EVENT(3, "validity intercept 0x%x for pid %u (kvm 0x%pK)", viwhy,
>  		  current->pid, vcpu->kvm);
>  
> -	/* do not warn on invalid runtime instrumentation mode */
> -	WARN_ONCE(viwhy != 0x44, "kvm: unhandled validity intercept 0x%x\n",
> -		  viwhy);
> +	/*
> +	 * Do not warn on:
> +	 *  - invalid runtime instrumentation mode
> +	 *  - PV related validities since they can be triggered by userspace
> +	 *    PV validities are in the 0x2XXX range
> +	 */
> +	WARN_ONCE(viwhy != 0x44 &&
> +		  ((viwhy < 0x2000) || (viwhy >= 0x3000)),
> +		  "kvm: unhandled validity intercept 0x%x\n", viwhy);
>  	return -EINVAL;
>  }
>