[PATCH v3 12/37] KVM: s390/mm: Make pages accessible before destroying the guest

Christian Borntraeger
2020-02-20T10:40:30Z

Before we destroy the secure configuration, we better make all
pages accessible again. This also happens during reboot, where we reboot
into a non-secure guest that then can go again into secure mode. As
this "new" secure guest will have a new ID we cannot reuse the old page
state.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
---
arch/s390/include/asm/gmap.h | 1 +
arch/s390/kvm/pv.c | 2 ++
arch/s390/mm/gmap.c | 35 +++++++++++++++++++++++++++++++++++
3 files changed, 38 insertions(+)

diff --git a/arch/s390/include/asm/gmap.h b/arch/s390/include/asm/gmap.h
index 6f9ff7a69fa2..a816fb4734b8 100644
--- a/arch/s390/include/asm/gmap.h
+++ b/arch/s390/include/asm/gmap.h
@@ -149,4 +149,5 @@ int gmap_mprotect_notify(struct gmap *, unsigned long start,
void gmap_sync_dirty_log_pmd(struct gmap *gmap, unsigned long dirty_bitmap[4],
unsigned long gaddr, unsigned long vmaddr);
int gmap_mark_unmergeable(void);
+void s390_reset_acc(struct mm_struct *mm);
#endif /* _ASM_S390_GMAP_H */
diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index 67ea9a18ed8f..7d95d7437140 100644
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -66,6 +66,8 @@ int kvm_s390_pv_destroy_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
{
int cc;

+ /* make all pages accessible before destroying the guest */
+ s390_reset_acc(kvm->mm);
cc = uv_cmd_nodata(kvm_s390_pv_get_handle(kvm),
UVC_CMD_DESTROY_SEC_CONF, rc, rrc);
WRITE_ONCE(kvm->arch.gmap->guest_handle, 0);
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 7291452fe5f0..27926a06df32 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -2650,3 +2650,38 @@ void s390_reset_cmma(struct mm_struct *mm)
up_write(&mm->mmap_sem);
}
EXPORT_SYMBOL_GPL(s390_reset_cmma);
+
+/*
+ * make inaccessible pages accessible again
+ */
+static int __s390_reset_acc(pte_t *ptep, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ pte_t pte = READ_ONCE(*ptep);
+
+ if (pte_present(pte))
+ WARN_ON_ONCE(uv_convert_from_secure(pte_val(pte) & PAGE_MASK));
+ return 0;
+}
+
+static const struct mm_walk_ops reset_acc_walk_ops = {
+ .pte_entry = __s390_reset_acc,
+};
+
+#include <linux/sched/mm.h>
+void s390_reset_acc(struct mm_struct *mm)
+{
+ /*
+ * we might be called during
+ * reset: we walk the pages and clear
+ * close of all kvm file descriptors: we walk the pages and clear
+ * exit of process on fd closure: vma already gone, do nothing
+ */
+ if (!mmget_not_zero(mm))
+ return;
+ down_read(&mm->mmap_sem);
+ walk_page_range(mm, 0, TASK_SIZE, &reset_acc_walk_ops, NULL);
+ up_read(&mm->mmap_sem);
+ mmput(mm);
+}
+EXPORT_SYMBOL_GPL(s390_reset_acc);
--
2.25.0