[PATCH v6 15/28] KVM: s390: KVM page table management functions: walks

Claudio Imbrenda
2025-12-22T16:51:12Z

Add page table management functions to be used for KVM guest (gmap)
page tables.

This patch adds functions to walk to specific table entries, or to
perform actions on a range of entries.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
arch/s390/kvm/dat.c | 386 ++++++++++++++++++++++++++++++++++++++++++++
arch/s390/kvm/dat.h | 39 +++++
2 files changed, 425 insertions(+)

diff --git a/arch/s390/kvm/dat.c b/arch/s390/kvm/dat.c
index a9d5b49ac411..3158652dbe8e 100644
--- a/arch/s390/kvm/dat.c
+++ b/arch/s390/kvm/dat.c
@@ -219,3 +219,389 @@ union pgste __dat_ptep_xchg(union pte *ptep, union pgste pgste, union pte new, g
WRITE_ONCE(*ptep, new);
return pgste;
}
+
+/*
+ * dat_split_ste - Split a segment table entry into page table entries
+ *
+ * Context: This function is assumed to be called with kvm->mmu_lock held.
+ *
+ * Return: 0 in case of success, -ENOMEM if running out of memory.
+ */
+static int dat_split_ste(struct kvm_s390_mmu_cache *mc, union pmd *pmdp, gfn_t gfn,
+ union asce asce, bool uses_skeys)
+{
+ union pgste pgste_init;
+ struct page_table *pt;
+ union pmd new, old;
+ union pte init;
+ int i;
+
+ BUG_ON(!mc);
+ old = READ_ONCE(*pmdp);
+
+ /* Already split, nothing to do */
+ if (!old.h.i && !old.h.fc)
+ return 0;
+
+ pt = dat_alloc_pt_noinit(mc);
+ if (!pt)
+ return -ENOMEM;
+ new.val = virt_to_phys(pt);
+
+ while (old.h.i || old.h.fc) {
+ init.val = pmd_origin_large(old);
+ init.h.p = old.h.p;
+ init.h.i = old.h.i;
+ init.s.d = old.s.fc1.d;
+ init.s.w = old.s.fc1.w;
+ init.s.y = old.s.fc1.y;
+ init.s.sd = old.s.fc1.sd;
+ init.s.pr = old.s.fc1.pr;
+ pgste_init.val = 0;
+ if (old.h.fc) {
+ for (i = 0; i < _PAGE_ENTRIES; i++)
+ pt->ptes[i].val = init.val | i * PAGE_SIZE;
+ /* no need to take locks as the page table is not installed yet */
+ pgste_init.prefix_notif = old.s.fc1.prefix_notif;
+ pgste_init.pcl = uses_skeys && init.h.i;
+ dat_init_pgstes(pt, pgste_init.val);
+ } else {
+ dat_init_page_table(pt, init.val, 0);
+ }
+
+ if (dat_pmdp_xchg_atomic(pmdp, old, new, gfn, asce)) {
+ if (!pgste_init.pcl)
+ return 0;
+ for (i = 0; i < _PAGE_ENTRIES; i++) {
+ union pgste pgste = pt->pgstes[i];
+
+ pgste = dat_save_storage_key_into_pgste(pt->ptes[i], pgste);
+ pgste_set_unlock(pt->ptes + i, pgste);
+ }
+ return 0;
+ }
+ old = READ_ONCE(*pmdp);
+ }
+
+ dat_free_pt(pt);
+ return 0;
+}
+
+/*
+ * dat_split_crste - Split a crste into smaller crstes
+ *
+ * Context: This function is assumed to be called with kvm->mmu_lock held.
+ *
+ * Return: 0 in case of success, -ENOMEM if running out of memory.
+ */
+static int dat_split_crste(struct kvm_s390_mmu_cache *mc, union crste *crstep,
+ gfn_t gfn, union asce asce, bool uses_skeys)
+{
+ struct crst_table *table;
+ union crste old, new, init;
+ int i;
+
+ old = READ_ONCE(*crstep);
+ if (is_pmd(old))
+ return dat_split_ste(mc, &crstep->pmd, gfn, asce, uses_skeys);
+
+ BUG_ON(!mc);
+
+ /* Already split, nothing to do */
+ if (!old.h.i && !old.h.fc)
+ return 0;
+
+ table = dat_alloc_crst_noinit(mc);
+ if (!table)
+ return -ENOMEM;
+
+ new.val = virt_to_phys(table);
+ new.h.tt = old.h.tt;
+ new.h.fc0.tl = _REGION_ENTRY_LENGTH;
+
+ while (old.h.i || old.h.fc) {
+ init = old;
+ init.h.tt--;
+ if (old.h.fc) {
+ for (i = 0; i < _CRST_ENTRIES; i++)
+ table->crstes[i].val = init.val | i * HPAGE_SIZE;
+ } else {
+ crst_table_init((void *)table, init.val);
+ }
+ if (dat_crstep_xchg_atomic(crstep, old, new, gfn, asce))
+ return 0;
+ old = READ_ONCE(*crstep);
+ }
+
+ dat_free_crst(table);
+ return 0;
+}
+
+/**
+ * dat_entry_walk() - walk the gmap page tables
+ * @mc: cache to use to allocate dat tables, if needed; can be NULL if neither
+ * @DAT_WALK_SPLIT or @DAT_WALK_ALLOC is specified.
+ * @gfn: guest frame
+ * @asce: the ASCE of the address space
+ * @flags: flags from WALK_* macros
+ * @walk_level: level to walk to, from LEVEL_* macros
+ * @last: will be filled the last visited non-pte DAT entry
+ * @ptepp: will be filled the last visited pte entry, if any, otherwise NULL
+ *
+ * Returns a table entry pointer for the given guest address and @level
+ *
+ * The @flags have the following meanings:
+ * * @DAT_WALK_IGN_HOLES: consider holes as normal table entries
+ * * @DAT_WALK_ALLOC: allocate new tables to reach the requested level, if needed
+ * * @DAT_WALK_SPLIT: split existing large pages to reach the requested level, if needed
+ * * @DAT_WALK_LEAF: return successfully whenever a large page is encountered
+ * * @DAT_WALK_ANY: return successfully even if the requested level could not be reached
+ * * @DAT_WALK_CONTINUE: walk to the requested level with the specified flags, and then try to
+ * continue walking to ptes with only DAT_WALK_ANY
+ * * @DAT_WALK_USES_SKEYS: storage keys are in use
+ *
+ * Context: called with kvm->mmu_lock held.
+ *
+ * Return:
+ * * PGM_ADDRESSING if the requested address lies outside memory
+ * * a PIC number if the requested address lies in a memory hole of type _DAT_TOKEN_PIC
+ * * -EFAULT if the requested address lies inside a memory hole of a different type
+ * * -EINVAL if the given ASCE is not compatible with the requested level
+ * * -EFBIG if the requested level could not be reached because a larger frame was found
+ * * -ENOENT if the requested level could not be reached for other reasons
+ * * -ENOMEM if running out of memory while allocating or splitting a table
+ */
+int dat_entry_walk(struct kvm_s390_mmu_cache *mc, gfn_t gfn, union asce asce, int flags,
+ int walk_level, union crste **last, union pte **ptepp)
+{
+ union vaddress vaddr = { .addr = gfn_to_gpa(gfn) };
+ bool continue_anyway = flags & DAT_WALK_CONTINUE;
+ bool uses_skeys = flags & DAT_WALK_USES_SKEYS;
+ bool ign_holes = flags & DAT_WALK_IGN_HOLES;
+ bool allocate = flags & DAT_WALK_ALLOC;
+ bool split = flags & DAT_WALK_SPLIT;
+ bool leaf = flags & DAT_WALK_LEAF;
+ bool any = flags & DAT_WALK_ANY;
+ struct page_table *pgtable;
+ struct crst_table *table;
+ union crste entry;
+ int rc;
+
+ *last = NULL;
+ *ptepp = NULL;
+ if (WARN_ON_ONCE(unlikely(!asce.val)))
+ return -EINVAL;
+ if (WARN_ON_ONCE(unlikely(walk_level > asce.dt)))
+ return -EINVAL;
+ if (!asce_contains_gfn(asce, gfn))
+ return PGM_ADDRESSING;
+
+ table = dereference_asce(asce);
+ if (asce.dt >= ASCE_TYPE_REGION1) {
+ *last = table->crstes + vaddr.rfx;
+ entry = READ_ONCE(**last);
+ if (WARN_ON_ONCE(entry.h.tt != TABLE_TYPE_REGION1))
+ return -EINVAL;
+ if (crste_hole(entry) && !ign_holes)
+ return entry.tok.type == _DAT_TOKEN_PIC ? entry.tok.par : -EFAULT;
+ if (walk_level == TABLE_TYPE_REGION1)
+ return 0;
+ if (entry.pgd.h.i) {
+ if (!allocate)
+ return any ? 0 : -ENOENT;
+ rc = dat_split_crste(mc, *last, gfn, asce, uses_skeys);
+ if (rc)
+ return rc;
+ entry = READ_ONCE(**last);
+ }
+ table = dereference_crste(entry.pgd);
+ }
+
+ if (asce.dt >= ASCE_TYPE_REGION2) {
+ *last = table->crstes + vaddr.rsx;
+ entry = READ_ONCE(**last);
+ if (WARN_ON_ONCE(entry.h.tt != TABLE_TYPE_REGION2))
+ return -EINVAL;
+ if (crste_hole(entry) && !ign_holes)
+ return entry.tok.type == _DAT_TOKEN_PIC ? entry.tok.par : -EFAULT;
+ if (walk_level == TABLE_TYPE_REGION2)
+ return 0;
+ if (entry.p4d.h.i) {
+ if (!allocate)
+ return any ? 0 : -ENOENT;
+ rc = dat_split_crste(mc, *last, gfn, asce, uses_skeys);
+ if (rc)
+ return rc;
+ entry = READ_ONCE(**last);
+ }
+ table = dereference_crste(entry.p4d);
+ }
+
+ if (asce.dt >= ASCE_TYPE_REGION3) {
+ *last = table->crstes + vaddr.rtx;
+ entry = READ_ONCE(**last);
+ if (WARN_ON_ONCE(entry.h.tt != TABLE_TYPE_REGION3))
+ return -EINVAL;
+ if (crste_hole(entry) && !ign_holes)
+ return entry.tok.type == _DAT_TOKEN_PIC ? entry.tok.par : -EFAULT;
+ if (walk_level == TABLE_TYPE_REGION3 &&
+ continue_anyway && !entry.pud.h.fc && !entry.h.i) {
+ walk_level = TABLE_TYPE_PAGE_TABLE;
+ allocate = false;
+ }
+ if (walk_level == TABLE_TYPE_REGION3 || ((leaf || any) && entry.pud.h.fc))
+ return 0;
+ if (entry.pud.h.i && !entry.pud.h.fc) {
+ if (!allocate)
+ return any ? 0 : -ENOENT;
+ rc = dat_split_crste(mc, *last, gfn, asce, uses_skeys);
+ if (rc)
+ return rc;
+ entry = READ_ONCE(**last);
+ }
+ if (walk_level <= TABLE_TYPE_SEGMENT && entry.pud.h.fc) {
+ if (!split)
+ return -EFBIG;
+ rc = dat_split_crste(mc, *last, gfn, asce, uses_skeys);
+ if (rc)
+ return rc;
+ entry = READ_ONCE(**last);
+ }
+ table = dereference_crste(entry.pud);
+ }
+
+ *last = table->crstes + vaddr.sx;
+ entry = READ_ONCE(**last);
+ if (WARN_ON_ONCE(entry.h.tt != TABLE_TYPE_SEGMENT))
+ return -EINVAL;
+ if (crste_hole(entry) && !ign_holes)
+ return entry.tok.type == _DAT_TOKEN_PIC ? entry.tok.par : -EFAULT;
+ if (continue_anyway && !entry.pmd.h.fc && !entry.h.i) {
+ walk_level = TABLE_TYPE_PAGE_TABLE;
+ allocate = false;
+ }
+ if (walk_level == TABLE_TYPE_SEGMENT || ((leaf || any) && entry.pmd.h.fc))
+ return 0;
+
+ if (entry.pmd.h.i && !entry.pmd.h.fc) {
+ if (!allocate)
+ return any ? 0 : -ENOENT;
+ rc = dat_split_ste(mc, &(*last)->pmd, gfn, asce, uses_skeys);
+ if (rc)
+ return rc;
+ entry = READ_ONCE(**last);
+ }
+ if (walk_level <= TABLE_TYPE_PAGE_TABLE && entry.pmd.h.fc) {
+ if (!split)
+ return -EFBIG;
+ rc = dat_split_ste(mc, &(*last)->pmd, gfn, asce, uses_skeys);
+ if (rc)
+ return rc;
+ entry = READ_ONCE(**last);
+ }
+ pgtable = dereference_pmd(entry.pmd);
+ *ptepp = pgtable->ptes + vaddr.px;
+ if (pte_hole(**ptepp) && !ign_holes)
+ return (*ptepp)->tok.type == _DAT_TOKEN_PIC ? (*ptepp)->tok.par : -EFAULT;
+ return 0;
+}
+
+static long dat_pte_walk_range(gfn_t gfn, gfn_t end, struct page_table *table, struct dat_walk *w)
+{
+ unsigned int idx = gfn & (_PAGE_ENTRIES - 1);
+ long rc = 0;
+
+ for ( ; gfn < end; idx++, gfn++) {
+ if (pte_hole(READ_ONCE(table->ptes[idx]))) {
+ if (!(w->flags & DAT_WALK_IGN_HOLES))
+ return -EFAULT;
+ if (!(w->flags & DAT_WALK_ANY))
+ continue;
+ }
+
+ rc = w->ops->pte_entry(table->ptes + idx, gfn, gfn + 1, w);
+ if (rc)
+ break;
+ }
+ return rc;
+}
+
+static long dat_crste_walk_range(gfn_t start, gfn_t end, struct crst_table *table,
+ struct dat_walk *walk)
+{
+ unsigned long idx, cur_shift, cur_size;
+ dat_walk_op the_op;
+ union crste crste;
+ gfn_t cur, next;
+ long rc = 0;
+
+ cur_shift = 8 + table->crstes[0].h.tt * 11;
+ idx = (start >> cur_shift) & (_CRST_ENTRIES - 1);
+ cur_size = 1UL << cur_shift;
+
+ for (cur = ALIGN_DOWN(start, cur_size); cur < end; idx++, cur = next) {
+ next = cur + cur_size;
+ walk->last = table->crstes + idx;
+ crste = READ_ONCE(*walk->last);
+
+ if (crste_hole(crste)) {
+ if (!(walk->flags & DAT_WALK_IGN_HOLES))
+ return -EFAULT;
+ if (!(walk->flags & DAT_WALK_ANY))
+ continue;
+ }
+
+ the_op = walk->ops->crste_ops[crste.h.tt];
+ if (the_op) {
+ rc = the_op(walk->last, cur, next, walk);
+ crste = READ_ONCE(*walk->last);
+ }
+ if (rc)
+ break;
+ if (!crste.h.i && !crste.h.fc) {
+ if (!is_pmd(crste))
+ rc = dat_crste_walk_range(max(start, cur), min(end, next),
+ _dereference_crste(crste), walk);
+ else if (walk->ops->pte_entry)
+ rc = dat_pte_walk_range(max(start, cur), min(end, next),
+ dereference_pmd(crste.pmd), walk);
+ }
+ }
+ return rc;
+}
+
+/**
+ * _dat_walk_gfn_range() - walk DAT tables
+ * @start: the first guest page frame to walk
+ * @end: the guest page frame immediately after the last one to walk
+ * @asce: the ASCE of the guest mapping
+ * @ops: the gmap_walk_ops that will be used to perform the walk
+ * @flags: flags from WALK_* (currently only WALK_IGN_HOLES is supported)
+ * @priv: will be passed as-is to the callbacks
+ *
+ * Any callback returning non-zero causes the walk to stop immediately.
+ *
+ * Return: -EINVAL in case of error, -EFAULT if @start is too high for the given
+ * asce unless the DAT_WALK_IGN_HOLES flag is specified, otherwise it
+ * returns whatever the callbacks return.
+ */
+long _dat_walk_gfn_range(gfn_t start, gfn_t end, union asce asce,
+ const struct dat_walk_ops *ops, int flags, void *priv)
+{
+ struct crst_table *table = dereference_asce(asce);
+ struct dat_walk walk = {
+ .ops = ops,
+ .asce = asce,
+ .priv = priv,
+ .flags = flags,
+ .start = start,
+ .end = end,
+ };
+
+ if (WARN_ON_ONCE(unlikely(!asce.val)))
+ return -EINVAL;
+ if (!asce_contains_gfn(asce, start))
+ return (flags & DAT_WALK_IGN_HOLES) ? 0 : -EFAULT;
+
+ return dat_crste_walk_range(start, min(end, asce_end(asce)), table, &walk);
+}
diff --git a/arch/s390/kvm/dat.h b/arch/s390/kvm/dat.h
index c0644021c92f..902d4a044067 100644
--- a/arch/s390/kvm/dat.h
+++ b/arch/s390/kvm/dat.h
@@ -45,6 +45,7 @@ enum {
#define TABLE_TYPE_PAGE_TABLE -1

enum dat_walk_flags {
+ DAT_WALK_USES_SKEYS = 0x40,
DAT_WALK_CONTINUE = 0x20,
DAT_WALK_IGN_HOLES = 0x10,
DAT_WALK_SPLIT = 0x08,
@@ -332,6 +333,34 @@ struct page_table {
static_assert(sizeof(struct crst_table) == _CRST_TABLE_SIZE);
static_assert(sizeof(struct page_table) == PAGE_SIZE);

+struct dat_walk;
+
+typedef long (*dat_walk_op)(union crste *crste, gfn_t gfn, gfn_t next, struct dat_walk *w);
+
+struct dat_walk_ops {
+ union {
+ dat_walk_op crste_ops[4];
+ struct {
+ dat_walk_op pmd_entry;
+ dat_walk_op pud_entry;
+ dat_walk_op p4d_entry;
+ dat_walk_op pgd_entry;
+ };
+ };
+ long (*pte_entry)(union pte *pte, gfn_t gfn, gfn_t next, struct dat_walk *w);
+};
+
+struct dat_walk {
+ const struct dat_walk_ops *ops;
+ union crste *last;
+ union pte *last_pte;
+ union asce asce;
+ gfn_t start;
+ gfn_t end;
+ int flags;
+ void *priv;
+};
+
/**
* _pte() - Useful constructor for union pte
* @pfn: the pfn this pte should point to.
@@ -436,6 +465,11 @@ bool dat_crstep_xchg_atomic(union crste *crstep, union crste old, union crste ne
union asce asce);
void dat_crstep_xchg(union crste *crstep, union crste new, gfn_t gfn, union asce asce);

+long _dat_walk_gfn_range(gfn_t start, gfn_t end, union asce asce,
+ const struct dat_walk_ops *ops, int flags, void *priv);
+
+int dat_entry_walk(struct kvm_s390_mmu_cache *mc, gfn_t gfn, union asce asce, int flags,
+ int walk_level, union crste **last, union pte **ptepp);
void dat_free_level(struct crst_table *table, bool owns_ptes);
struct crst_table *dat_alloc_crst_sleepable(unsigned long init);

@@ -834,4 +868,9 @@ static inline void dat_crstep_clear(union crste *crstep, gfn_t gfn, union asce a
dat_crstep_xchg(crstep, newcrste, gfn, asce);
}

+static inline int get_level(union crste *crstep, union pte *ptep)
+{
+ return ptep ? TABLE_TYPE_PAGE_TABLE : crstep->h.tt;
+}
+
#endif /* __KVM_S390_DAT_H */
--
2.52.0