[PATCH v2 05/20] KVM: s390: Add helper functions for fault handling

Claudio Imbrenda
2025-09-10T18:07:54Z

Add some helper functions for handling multiple guest faults at the
same time.

This will be needed for VSIE, where a nested guest access also needs to
access all the page tables that map it.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
arch/s390/kvm/gaccess.h | 14 ++++++++++
arch/s390/kvm/kvm-s390.c | 44 +++++++++++++++++++++++++++++++
arch/s390/kvm/kvm-s390.h | 56 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 114 insertions(+)

diff --git a/arch/s390/kvm/gaccess.h b/arch/s390/kvm/gaccess.h
index 3fde45a151f2..9c82f7460821 100644
--- a/arch/s390/kvm/gaccess.h
+++ b/arch/s390/kvm/gaccess.h
@@ -457,4 +457,18 @@ int kvm_s390_check_low_addr_prot_real(struct kvm_vcpu *vcpu, unsigned long gra);
int kvm_s390_shadow_fault(struct kvm_vcpu *vcpu, struct gmap *shadow,
unsigned long saddr, unsigned long *datptr);

+static inline int __kvm_s390_faultin_read_gpa(struct kvm *kvm, struct guest_fault *f, gpa_t gaddr,
+ unsigned long *val)
+{
+ phys_addr_t phys_addr;
+ int rc;
+
+ rc = __kvm_s390_faultin_gfn(kvm, f, gpa_to_gfn(gaddr), false);
+ if (!rc) {
+ phys_addr = PFN_PHYS(f->pfn) | offset_in_page(gaddr);
+ *val = *(unsigned long *)phys_to_virt(phys_addr);
+ }
+ return rc;
+}
+
#endif /* __KVM_S390_GACCESS_H */
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 61aa64886c36..af8a62abec48 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -4858,6 +4858,50 @@ static void kvm_s390_assert_primary_as(struct kvm_vcpu *vcpu)
current->thread.gmap_int_code, current->thread.gmap_teid.val);
}

+/**
+ * __kvm_s390_faultin_gfn() - fault in and pin a guest address
+ * @kvm: the guest
+ * @guest_fault: will be filled with information on the pin operation
+ * @gfn: guest frame
+ * @wr: if true indicates a write access
+ *
+ * Fault in and pin a guest address using absolute addressing, and without
+ * marking the page referenced.
+ *
+ * Context: Called with mm->mmap_lock in read mode.
+ *
+ * Return:
+ * * 0 in case of success,
+ * * -EFAULT if reading using the virtual address failed,
+ * * -EINTR if a signal is pending,
+ * * -EAGAIN if FOLL_NOWAIT was specified, but IO is needed
+ * * PGM_ADDRESSING if the guest address lies outside of guest memory.
+ */
+int __kvm_s390_faultin_gfn(struct kvm *kvm, struct guest_fault *guest_fault, gfn_t gfn, bool wr)
+{
+ struct kvm_memory_slot *slot;
+ kvm_pfn_t pfn;
+ int foll;
+
+ foll = wr ? FOLL_WRITE : 0;
+ slot = gfn_to_memslot(kvm, gfn);
+ pfn = __kvm_faultin_pfn(slot, gfn, foll, &guest_fault->writable, &guest_fault->page);
+ if (is_noslot_pfn(pfn))
+ return PGM_ADDRESSING;
+ if (is_sigpending_pfn(pfn))
+ return -EINTR;
+ if (pfn == KVM_PFN_ERR_NEEDS_IO)
+ return -EAGAIN;
+ if (is_error_pfn(pfn))
+ return -EFAULT;
+
+ guest_fault->pfn = pfn;
+ guest_fault->gfn = gfn;
+ guest_fault->write_attempt = wr;
+ guest_fault->valid = true;
+ return 0;
+}
+
/*
* __kvm_s390_handle_dat_fault() - handle a dat fault for the gmap of a vcpu
* @vcpu: the vCPU whose gmap is to be fixed up
diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index c44fe0c3a097..dabcf65f58ff 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -22,6 +22,15 @@

#define KVM_S390_UCONTROL_MEMSLOT (KVM_USER_MEM_SLOTS + 0)

+struct guest_fault {
+ gfn_t gfn; /* Guest frame */
+ kvm_pfn_t pfn; /* Host PFN */
+ struct page *page; /* Host page */
+ bool writable; /* Mapping is writable */
+ bool write_attempt; /* Write access attempted */
+ bool valid; /* This entry contains valid data */
+};
+
static inline void kvm_s390_fpu_store(struct kvm_run *run)
{
fpu_stfpc(&run->s.regs.fpc);
@@ -464,12 +473,59 @@ int kvm_s390_cpus_from_pv(struct kvm *kvm, u16 *rc, u16 *rrc);
int __kvm_s390_handle_dat_fault(struct kvm_vcpu *vcpu, gfn_t gfn, gpa_t gaddr, unsigned int flags);
int __kvm_s390_mprotect_many(struct gmap *gmap, gpa_t gpa, u8 npages, unsigned int prot,
unsigned long bits);
+int __kvm_s390_faultin_gfn(struct kvm *kvm, struct guest_fault *f, gfn_t gfn, bool wr);

static inline int kvm_s390_handle_dat_fault(struct kvm_vcpu *vcpu, gpa_t gaddr, unsigned int flags)
{
return __kvm_s390_handle_dat_fault(vcpu, gpa_to_gfn(gaddr), gaddr, flags);
}

+static inline void release_faultin_multiple(struct kvm *kvm, struct guest_fault *guest_faults,
+ int n, bool ignore)
+{
+ int i;
+
+ for (i = 0; i < n; i++) {
+ kvm_release_faultin_page(kvm, guest_faults[i].page, ignore,
+ guest_faults[i].write_attempt);
+ guest_faults[i].page = NULL;
+ }
+}
+
+static inline bool __kvm_s390_multiple_faults_need_retry(struct kvm *kvm, unsigned long seq,
+ struct guest_fault *guest_faults, int n,
+ bool unsafe)
+{
+ int i;
+
+ for (i = 0; i < n; i++) {
+ if (!guest_faults[i].valid)
+ continue;
+ if ((unsafe && mmu_invalidate_retry_gfn_unsafe(kvm, seq, guest_faults[i].gfn)) ||
+ (!unsafe && mmu_invalidate_retry_gfn(kvm, seq, guest_faults[i].gfn))) {
+ release_faultin_multiple(kvm, guest_faults, n, true);
+ return true;
+ }
+ }
+ return false;
+}
+
+static inline int __kvm_s390_faultin_gfn_range(struct kvm *kvm, struct guest_fault *guest_faults,
+ gfn_t start, int n_pages, bool write_attempt)
+{
+ int i, rc = 0;
+
+ for (i = 0; !rc && i < n_pages; i++)
+ rc = __kvm_s390_faultin_gfn(kvm, guest_faults + i, start + i, write_attempt);
+ return rc;
+}
+
+#define release_faultin_array(kvm, array, ignore) \
+ release_faultin_multiple(kvm, array, ARRAY_SIZE(array), ignore)
+
+#define __kvm_s390_fault_array_needs_retry(kvm, seq, array, unsafe) \
+ __kvm_s390_multiple_faults_need_retry(kvm, seq, array, ARRAY_SIZE(array), unsafe)
+
/* implemented in diag.c */
int kvm_s390_handle_diag(struct kvm_vcpu *vcpu);

--
2.51.0