[PATCH v2 1/4] KVM: s390: Minor refactor of base/ext facility lists

Christoph Schlameuss
2026-02-26T12:49:39Z

Directly use the size of the arrays instead of going through the
indirection of kvm_s390_fac_size().
Don't use magic number for the number of entries in the non hypervisor
managed facility bit mask list.
Make the constraint of that number on kvm_s390_fac_base obvious.
Get rid of implicit double anding of stfle_fac_list.

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>
---
arch/s390/kvm/kvm-s390.c | 44 +++++++++++++++++++-------------------------
1 file changed, 19 insertions(+), 25 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 7a175d86cef0359ec71b6b631b5808e9f626fb9e..1a4abac697a40079c4dd6566581aaed321871a1f 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -232,33 +232,25 @@ static int async_destroy = 1;
module_param(async_destroy, int, 0444);
MODULE_PARM_DESC(async_destroy, "Asynchronous destroy for protected guests");

-/*
- * For now we handle at most 16 double words as this is what the s390 base
- * kernel handles and stores in the prefix page. If we ever need to go beyond
- * this, this requires changes to code, but the external uapi can stay.
- */
-#define SIZE_INTERNAL 16
-
+#define HMFAI_DWORDS 16
/*
* Base feature mask that defines default mask for facilities. Consists of the
* defines in FACILITIES_KVM and the non-hypervisor managed bits.
*/
-static unsigned long kvm_s390_fac_base[SIZE_INTERNAL] = { FACILITIES_KVM };
+static unsigned long kvm_s390_fac_base[HMFAI_DWORDS] = { FACILITIES_KVM };
+static_assert(ARRAY_SIZE(((long[]){ FACILITIES_KVM })) <= HMFAI_DWORDS);
+static_assert(ARRAY_SIZE(kvm_s390_fac_base) <= S390_ARCH_FAC_MASK_SIZE_U64);
+static_assert(ARRAY_SIZE(kvm_s390_fac_base) <= S390_ARCH_FAC_LIST_SIZE_U64);
+static_assert(ARRAY_SIZE(kvm_s390_fac_base) <= ARRAY_SIZE(stfle_fac_list));
+
/*
* Extended feature mask. Consists of the defines in FACILITIES_KVM_CPUMODEL
* and defines the facilities that can be enabled via a cpu model.
*/
-static unsigned long kvm_s390_fac_ext[SIZE_INTERNAL] = { FACILITIES_KVM_CPUMODEL };
-
-static unsigned long kvm_s390_fac_size(void)
-{
- BUILD_BUG_ON(SIZE_INTERNAL > S390_ARCH_FAC_MASK_SIZE_U64);
- BUILD_BUG_ON(SIZE_INTERNAL > S390_ARCH_FAC_LIST_SIZE_U64);
- BUILD_BUG_ON(SIZE_INTERNAL * sizeof(unsigned long) >
- sizeof(stfle_fac_list));
-
- return SIZE_INTERNAL;
-}
+static const unsigned long kvm_s390_fac_ext[] = { FACILITIES_KVM_CPUMODEL };
+static_assert(ARRAY_SIZE(kvm_s390_fac_ext) <= S390_ARCH_FAC_MASK_SIZE_U64);
+static_assert(ARRAY_SIZE(kvm_s390_fac_ext) <= S390_ARCH_FAC_LIST_SIZE_U64);
+static_assert(ARRAY_SIZE(kvm_s390_fac_ext) <= ARRAY_SIZE(stfle_fac_list));

/* available cpu features supported by kvm */
static DECLARE_BITMAP(kvm_s390_available_cpu_feat, KVM_S390_VM_CPU_FEAT_NR_BITS);
@@ -3212,13 +3204,16 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
kvm->arch.sie_page2->kvm = kvm;
kvm->arch.model.fac_list = kvm->arch.sie_page2->fac_list;

- for (i = 0; i < kvm_s390_fac_size(); i++) {
+ for (i = 0; i < ARRAY_SIZE(kvm_s390_fac_base); i++) {
kvm->arch.model.fac_mask[i] = stfle_fac_list[i] &
- (kvm_s390_fac_base[i] |
- kvm_s390_fac_ext[i]);
+ kvm_s390_fac_base[i];
kvm->arch.model.fac_list[i] = stfle_fac_list[i] &
kvm_s390_fac_base[i];
}
+ for (i = 0; i < ARRAY_SIZE(kvm_s390_fac_ext); i++) {
+ kvm->arch.model.fac_mask[i] |= stfle_fac_list[i] &
+ kvm_s390_fac_ext[i];
+ }
kvm->arch.model.subfuncs = kvm_s390_available_subfunc;

/* we are always in czam mode - even on pre z14 machines */
@@ -5788,9 +5783,8 @@ static int __init kvm_s390_init(void)
return -ENODEV;
}

- for (i = 0; i < 16; i++)
- kvm_s390_fac_base[i] |=
- stfle_fac_list[i] & nonhyp_mask(i);
+ for (i = 0; i < HMFAI_DWORDS; i++)
+ kvm_s390_fac_base[i] |= nonhyp_mask(i);

r = __kvm_s390_init();
if (r)

--
2.53.0