Re: [PATCH 4/4] KVM: s390: vsie: Implement ASTFLEIE facility 2

["Christoph Schlameuss" <schlameuss@linux.ibm.com>]

On Fri Feb 20, 2026 at 11:07 AM CET, Janosch Frank wrote:
> On 2/12/26 10:24, Christoph Schlameuss wrote:
>> From: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
>> 
>> Implement shadowing of format-2 facility list when running in VSIE.
>> 
>> ASTFLEIE2 is available since IBM z16.
>> To function G1 has to run this KVM code and G1 and G2 have to run QEMU
>> with ASTFLEIE2 support.
>> 
>> Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
>> Co-developed-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
>> Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
>> ---
>
> [...]
>
>> +static int handle_stfle_2(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page,
>> +			  u32 fac_list_origin)
>> +{
>> +	struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
>> +	u8 *shadow_fac = &vsie_page->fac[0];
>> +	u64 len;
>> +
>> +	if (read_guest_real(vcpu, fac_list_origin, &len, sizeof(len)))
>> +		return set_validity_icpt(scb_s, 0x1090U);
>> +	fac_list_origin += sizeof(len);
>> +	len = (len & 0xff);
>> +	memcpy(shadow_fac, &len, sizeof(len)); /* discard reserved bits */
>> +	shadow_fac += sizeof(len);
>
> You can choose between adding a struct for the new format and what you 
> did here. Is this really the better option?
>
>
> Add the struct and add a constant for the format 2 format control used 
> in the second to last line of this function while you're at it.
>

Will do.

>> +	len += 1;
>> +	/* assert no overflow with maximum len */
>> +	BUILD_BUG_ON(sizeof(vsie_page->fac) < 257 * sizeof(u64));> +	if (read_guest_real(vcpu, fac_list_origin, shadow_fac, len * 
> sizeof(u64)))
>> +		return set_validity_icpt(scb_s, 0x1090U);
>
> Sprinkle in some \n between the build bugs and code or just move them to 
> the top as one block.
> I'd much rather have build bugs at the top of the function than inside 
> the code.
>
>> +	BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct vsie_page, fac), 8));
>
> That was already added last patch, no?
>

Yes, it was. Keeping the one in handle_stfle(). We actually can put both newly
introduced build bug macros there.

>> +	scb_s->fac = (u32)virt_to_phys(&vsie_page->fac) | 2;
>> +	return 0;
>> +}
>> +
>>   /*
>>    * Try to shadow + enable the guest 2 provided facility list.
>>    * Retry instruction execution if enabled for and provided by guest 2.
>> @@ -1057,9 +1080,11 @@ static int handle_stfle(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>>   		case 0:
>>   			return handle_stfle_0(vcpu, vsie_page, fac_list_origin);
>>   		case 1:
>> +			return set_validity_icpt(&vsie_page->scb_s, 0x1330U);
>>   		case 2:
>> +			return handle_stfle_2(vcpu, vsie_page, fac_list_origin);
>>   		case 3:
>> -			unreachable();
>> +			return set_validity_icpt(&vsie_page->scb_s, 0x1330U);
>>   		}
>>   	}
>>   	return 0;
>>