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

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

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