On 9/11/25 3:19 PM, Claudio Imbrenda wrote:
On Thu, 11 Sep 2025 14:57:40 +0200
Janosch Frank <frankja@xxxxxxxxxxxxx> wrote:
On 9/10/25 8:07 PM, Claudio Imbrenda wrote:
Add page table management functions to be used for KVM guest (gmap)
page tables.
This patch adds functions to clear, replace or exchange DAT table
entries.
Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
---
arch/s390/kvm/dat.c | 120 ++++++++++++++++++++++++++++++++++++++++++++
arch/s390/kvm/dat.h | 40 +++++++++++++++
2 files changed, 160 insertions(+)
diff --git a/arch/s390/kvm/dat.c b/arch/s390/kvm/dat.c
index 326be78adcda..f26e3579bd77 100644
--- a/arch/s390/kvm/dat.c
+++ b/arch/s390/kvm/dat.c
@@ -89,3 +89,123 @@ void dat_free_level(struct crst_table *table, bool owns_ptes)
}
dat_free_crst(table);
}
+
+/**
+ * dat_crstep_xchg - exchange a guest CRST with another
+ * @crstep: pointer to the CRST entry
+ * @new: replacement entry
+ * @gfn: the affected guest address
+ * @asce: the ASCE of the address space
+ *
+ * This function is assumed to be called with the guest_table_lock
+ * held.
+ */
+void dat_crstep_xchg(union crste *crstep, union crste new, gfn_t gfn, union asce asce)
+{
+ if (crstep->h.i) {
+ WRITE_ONCE(*crstep, new);
+ return;
+ } else if (cpu_has_edat2()) {
+ crdte_crste(crstep, *crstep, new, gfn, asce);
+ return;
+ }
+
+ if (machine_has_tlb_guest())
+ idte_crste(crstep, gfn, IDTE_GUEST_ASCE, asce, IDTE_GLOBAL);
+ else if (cpu_has_idte())
+ idte_crste(crstep, gfn, 0, NULL_ASCE, IDTE_GLOBAL);
+ else
+ csp_invalidate_crste(crstep);
I'm wondering if we can make stfle 3 (DTE) a requirement for KVM or
Linux as a whole since it was introduced with z990 AFAIK.
AFAIK we don't support machines older than z10 anyway
but in that case we can only get rid of csp_invalidate_crste(), which
is not much.
I can remove it, if you really think it's ugly
That was more of a general question, I think we have more of those
checks in non-kvm code. Your code is fine as is.
+ WRITE_ONCE(*crstep, new);
+}
+
+/**
+ * dat_crstep_xchg_atomic - exchange a gmap pmd with another
+ * @crstep: pointer to the crste entry
+ * @old: expected old value
+ * @new: replacement entry
+ * @gfn: the affected guest address
+ * @asce: the asce of the address space
+ *
+ * This function should only be called on invalid crstes, or on crstes with
+ * FC = 1, as that guarantees the presence of CSPG.
+ *
+ * Return: true if the exchange was successful.
+ */
+bool dat_crstep_xchg_atomic(union crste *crstep, union crste old, union crste new, gfn_t gfn,
+ union asce asce)
+{
+ if (old.h.i)
+ return arch_try_cmpxchg((long *)crstep, &old.val, new.val);
+ if (cpu_has_edat2())
+ return crdte_crste(crstep, old, new, gfn, asce);
+ if (cpu_has_idte())
+ return cspg_crste(crstep, old, new);
+
+ WARN_ONCE(1, "Machine does not have CSPG and DAT table was not invalid.");
+ return false;
+}
