[PATCH v1 2/2] KVM: s390: pv: fix race when making a page secure

[Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>]

Holding the pte lock for the page that is being converted to secure is
needed to avoid races. A previous commit removed the locking, which
caused issues. Fix by locking the pte again.

Fixes: 5cbe24350b7d ("KVM: s390: move pv gmap functions into kvm")
Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
---
 arch/s390/include/asm/uv.h |  2 +-
 arch/s390/kernel/uv.c      | 19 +++++++++++++++++--
 arch/s390/kvm/gmap.c       | 12 ++++++++----
 3 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
index b11f5b6d0bd1..46fb0ef6f984 100644
--- a/arch/s390/include/asm/uv.h
+++ b/arch/s390/include/asm/uv.h
@@ -631,7 +631,7 @@ int uv_pin_shared(unsigned long paddr);
 int uv_destroy_folio(struct folio *folio);
 int uv_destroy_pte(pte_t pte);
 int uv_convert_from_secure_pte(pte_t pte);
-int make_folio_secure(struct folio *folio, struct uv_cb_header *uvcb);
+int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header *uvcb);
 int uv_convert_from_secure(unsigned long paddr);
 int uv_convert_from_secure_folio(struct folio *folio);
 
diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index 9f05df2da2f7..de3c092da7b9 100644
--- a/arch/s390/kernel/uv.c
+++ b/arch/s390/kernel/uv.c
@@ -245,7 +245,7 @@ static int expected_folio_refs(struct folio *folio)
  * Context: The caller must hold exactly one extra reference on the folio
  *          (it's the same logic as split_folio())
  */
-int make_folio_secure(struct folio *folio, struct uv_cb_header *uvcb)
+static int __make_folio_secure(struct folio *folio, unsigned long hva, struct uv_cb_header *uvcb)
 {
 	int expected, cc = 0;
 
@@ -277,7 +277,22 @@ int make_folio_secure(struct folio *folio, struct uv_cb_header *uvcb)
 		return -EAGAIN;
 	return uvcb->rc == 0x10a ? -ENXIO : -EINVAL;
 }
-EXPORT_SYMBOL_GPL(make_folio_secure);
+
+int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header *uvcb)
+{
+	spinlock_t *ptelock;
+	pte_t *ptep;
+	int rc;
+
+	ptep = get_locked_pte(mm, hva, &ptelock);
+	if (!ptep)
+		return -ENXIO;
+	rc = __make_folio_secure(page_folio(pte_page(*ptep)), hva, uvcb);
+	pte_unmap_unlock(ptep, ptelock);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(make_hva_secure);
 
 /*
  * To be called with the folio locked or with an extra reference! This will
diff --git a/arch/s390/kvm/gmap.c b/arch/s390/kvm/gmap.c
index fc4d490d25a2..e56c0ab5fec7 100644
--- a/arch/s390/kvm/gmap.c
+++ b/arch/s390/kvm/gmap.c
@@ -55,7 +55,7 @@ static bool should_export_before_import(struct uv_cb_header *uvcb, struct mm_str
 	return atomic_read(&mm->context.protected_count) > 1;
 }
 
-static int __gmap_make_secure(struct gmap *gmap, struct page *page, void *uvcb)
+static int __gmap_make_secure(struct gmap *gmap, struct page *page, unsigned long hva, void *uvcb)
 {
 	struct folio *folio = page_folio(page);
 	int rc;
@@ -83,7 +83,7 @@ static int __gmap_make_secure(struct gmap *gmap, struct page *page, void *uvcb)
 		return -EAGAIN;
 	if (should_export_before_import(uvcb, gmap->mm))
 		uv_convert_from_secure(folio_to_phys(folio));
-	rc = make_folio_secure(folio, uvcb);
+	rc = make_hva_secure(gmap->mm, hva, uvcb);
 	folio_unlock(folio);
 
 	/*
@@ -120,6 +120,7 @@ static int __gmap_make_secure(struct gmap *gmap, struct page *page, void *uvcb)
 int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb)
 {
 	struct kvm *kvm = gmap->private;
+	unsigned long vmaddr;
 	struct page *page;
 	int rc = 0;
 
@@ -127,8 +128,11 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb)
 
 	page = gfn_to_page(kvm, gpa_to_gfn(gaddr));
 	mmap_read_lock(gmap->mm);
-	if (page)
-		rc = __gmap_make_secure(gmap, page, uvcb);
+	vmaddr = gfn_to_hva(gmap->private, gpa_to_gfn(gaddr));
+	if (kvm_is_error_hva(vmaddr))
+		rc = -ENXIO;
+	if (!rc && page)
+		rc = __gmap_make_secure(gmap, page, vmaddr, uvcb);
 	kvm_release_page_clean(page);
 	mmap_read_unlock(gmap->mm);
 
-- 
2.48.1