Re: [PATCH RFC v2 01/11] KVM: s390: Add SCAO read and write helpers

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

On Mon, 10 Nov 2025 18:16:41 +0100
Christoph Schlameuss <schlameuss@linux.ibm.com> wrote:

> Introduce some small helper functions to get and set the system control
> area origin address from the SIE control block.
> 
> Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
> ---
>  arch/s390/kvm/vsie.c | 29 +++++++++++++++++++++--------
>  1 file changed, 21 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 347268f89f2f186bea623a3adff7376cabc305b2..ced2ca4ce5b584403d900ed11cb064919feda8e9 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -123,6 +123,23 @@ static int prefix_is_mapped(struct vsie_page *vsie_page)
>  	return !(atomic_read(&vsie_page->scb_s.prog20) & PROG_REQUEST);
>  }
>  
> +static gpa_t read_scao(struct kvm *kvm, struct kvm_s390_sie_block *scb)
> +{
> +	gpa_t sca;

is it, though?

> +
> +	sca = READ_ONCE(scb->scaol) & ~0xfUL;
> +	if (test_kvm_cpu_feat(kvm, KVM_S390_VM_CPU_FEAT_64BSCAO))
> +		sca |= (u64)READ_ONCE(scb->scaoh) << 32;

this feels more like an hpa_t, which is what you also use in the
function below

> +
> +	return sca;
> +}
> +
> +static void write_scao(struct kvm_s390_sie_block *scb, hpa_t hpa)
> +{
> +	scb->scaoh = (u32)((u64)hpa >> 32);
> +	scb->scaol = (u32)(u64)hpa;
> +}
> +
>  /* copy the updated intervention request bits into the shadow scb */
>  static void update_intervention_requests(struct vsie_page *vsie_page)
>  {
> @@ -714,12 +731,11 @@ static void unpin_blocks(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>  	struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
>  	hpa_t hpa;
>  
> -	hpa = (u64) scb_s->scaoh << 32 | scb_s->scaol;
> +	hpa = read_scao(vcpu->kvm, scb_s);
>  	if (hpa) {
>  		unpin_guest_page(vcpu->kvm, vsie_page->sca_gpa, hpa);
>  		vsie_page->sca_gpa = 0;
> -		scb_s->scaol = 0;
> -		scb_s->scaoh = 0;
> +		write_scao(scb_s, 0);
>  	}
>  
>  	hpa = scb_s->itdba;
> @@ -773,9 +789,7 @@ static int pin_blocks(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>  	gpa_t gpa;
>  	int rc = 0;
>  
> -	gpa = READ_ONCE(scb_o->scaol) & ~0xfUL;
> -	if (test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_64BSCAO))
> -		gpa |= (u64) READ_ONCE(scb_o->scaoh) << 32;
> +	gpa = read_scao(vcpu->kvm, scb_o);
>  	if (gpa) {
>  		if (gpa < 2 * PAGE_SIZE)
>  			rc = set_validity_icpt(scb_s, 0x0038U);
> @@ -792,8 +806,7 @@ static int pin_blocks(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>  		if (rc)
>  			goto unpin;
>  		vsie_page->sca_gpa = gpa;
> -		scb_s->scaoh = (u32)((u64)hpa >> 32);
> -		scb_s->scaol = (u32)(u64)hpa;
> +		write_scao(scb_s, hpa);
>  	}
>  
>  	gpa = READ_ONCE(scb_o->itdba) & ~0xffUL;
>