[PATCH v2 3/4] KVM: s390: vsie: Refactor handle_stfle

Christoph Schlameuss
2026-02-26T12:49:40Z

Use switch case in anticipation of handling format-1 and format-2
facility list designations in the future.
As the alternate STFLE facilities are not enabled, only case 0 is
possible.
No functional change intended.

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/include/asm/kvm_host.h | 2 ++
arch/s390/include/uapi/asm/kvm.h | 1 +
arch/s390/kvm/vsie.c | 53 ++++++++++++++++++++++++++++------------
3 files changed, 40 insertions(+), 16 deletions(-)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 64a50f0862aabb994089090c750bd312a7233e2c..23d17700319a5ef2031eabcad34b6191d1ef9b21 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -484,6 +484,8 @@ struct s390_io_adapter {
#define MAX_S390_IO_ADAPTERS ((MAX_ISC + 1) * 8)
#define MAX_S390_ADAPTER_MAPS 256

+#define S390_ARCH_FAC_ORIGIN_MASK 0x7ffffff8U
+
/* maximum size of facilities and facility mask is 2k bytes */
#define S390_ARCH_FAC_LIST_SIZE_BYTE (1<<11)
#define S390_ARCH_FAC_LIST_SIZE_U64 \
diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
index 60345dd2cba2d611b76f8b5c70eab8f0abab4b9b..4192769b5ce069ba28d00d7cf1c4f1b34037d633 100644
--- a/arch/s390/include/uapi/asm/kvm.h
+++ b/arch/s390/include/uapi/asm/kvm.h
@@ -444,6 +444,7 @@ struct kvm_s390_vm_cpu_machine {
#define KVM_S390_VM_CPU_FEAT_PFMFI 11
#define KVM_S390_VM_CPU_FEAT_SIGPIF 12
#define KVM_S390_VM_CPU_FEAT_KSS 13
+#define KVM_S390_VM_CPU_FEAT_ASTFLEIE2 14
struct kvm_s390_vm_cpu_feat {
__u64 feat[16];
};
diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index d249b10044eb7595295fc20e9287e0629958d896..3a2c644ef4fc630e2a13475fc1600c8053520bcd 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -6,12 +6,15 @@
*
* Author(s): David Hildenbrand <dahi@linux.vnet.ibm.com>
*/
+#include <linux/align.h>
#include <linux/vmalloc.h>
#include <linux/kvm_host.h>
#include <linux/bug.h>
+#include <linux/compiler.h>
#include <linux/list.h>
#include <linux/bitmap.h>
#include <linux/sched/signal.h>
+#include <linux/stddef.h>
#include <linux/io.h>
#include <linux/mman.h>

@@ -979,6 +982,23 @@ static void retry_vsie_icpt(struct vsie_page *vsie_page)
clear_vsie_icpt(vsie_page);
}

+static int handle_stfle_0(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page,
+ u32 fac_list_origin)
+{
+ struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
+
+ /*
+ * format-0 -> size of nested guest's facility list == guest's size
+ * guest's size == host's size, since STFLE is interpretatively executed
+ * using a format-0 for the guest, too.
+ */
+ if (read_guest_real(vcpu, fac_list_origin, &vsie_page->fac,
+ stfle_size() * sizeof(u64)))
+ return set_validity_icpt(scb_s, 0x1090U);
+ scb_s->fac = (u32)virt_to_phys(&vsie_page->fac);
+ return 0;
+}
+
/*
* Try to shadow + enable the guest 2 provided facility list.
* Retry instruction execution if enabled for and provided by guest 2.
@@ -988,29 +1008,30 @@ static void retry_vsie_icpt(struct vsie_page *vsie_page)
*/
static int handle_stfle(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
{
- struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
- __u32 fac = READ_ONCE(vsie_page->scb_o->fac);
+ bool has_astfleie2 = test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_ASTFLEIE2);
+ u32 fac = READ_ONCE(vsie_page->scb_o->fac);
+ int format_mask, format;
+ u32 origin;
+
+ BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct vsie_page, fac), 8));

- /*
- * Alternate-STFLE-Interpretive-Execution facilities are not supported
- * -> format-0 flcb
- */
if (fac && test_kvm_facility(vcpu->kvm, 7)) {
retry_vsie_icpt(vsie_page);
/*
* The facility list origin (FLO) is in bits 1 - 28 of the FLD
* so we need to mask here before reading.
*/
- fac = fac & 0x7ffffff8U;
- /*
- * format-0 -> size of nested guest's facility list == guest's size
- * guest's size == host's size, since STFLE is interpretatively executed
- * using a format-0 for the guest, too.
- */
- if (read_guest_real(vcpu, fac, &vsie_page->fac,
- stfle_size() * sizeof(u64)))
- return set_validity_icpt(scb_s, 0x1090U);
- scb_s->fac = (u32)virt_to_phys(&vsie_page->fac);
+ origin = fac & S390_ARCH_FAC_ORIGIN_MASK;
+ format_mask = has_astfleie2 ? 3 : 0;
+ format = fac & format_mask;
+ switch (format) {
+ case 0:
+ return handle_stfle_0(vcpu, vsie_page, origin);
+ case 1:
+ case 2:
+ case 3:
+ unreachable();
+ }
}
return 0;
}

--
2.53.0