[PATCH v6 08/28] s390/mm: Warn if uv_convert_from_secure_pte() fails

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

If uv_convert_from_secure_pte() fails, the page becomes unusable by the
host. The failure can only occour in case of hardware malfunction or a
serious KVM bug.

When the unusable page is reused, the system can have issues and
hang.

Print a warning to aid debugging such unlikely scenarios.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/include/asm/pgtable.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 73c30b811b98..04335f5e7f47 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1239,7 +1239,7 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
 	res = ptep_xchg_lazy(mm, addr, ptep, __pte(_PAGE_INVALID));
 	/* At this point the reference through the mapping is still present */
 	if (mm_is_protected(mm) && pte_present(res))
-		uv_convert_from_secure_pte(res);
+		WARN_ON_ONCE(uv_convert_from_secure_pte(res));
 	return res;
 }
 
@@ -1257,7 +1257,7 @@ static inline pte_t ptep_clear_flush(struct vm_area_struct *vma,
 	res = ptep_xchg_direct(vma->vm_mm, addr, ptep, __pte(_PAGE_INVALID));
 	/* At this point the reference through the mapping is still present */
 	if (mm_is_protected(vma->vm_mm) && pte_present(res))
-		uv_convert_from_secure_pte(res);
+		WARN_ON_ONCE(uv_convert_from_secure_pte(res));
 	return res;
 }
 
@@ -1294,9 +1294,10 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
 	/*
 	 * If something went wrong and the page could not be destroyed, or
 	 * if this is not a mm teardown, the slower export is used as
-	 * fallback instead.
+	 * fallback instead. If even that fails, print a warning and leak
+	 * the page, to avoid crashing the whole system.
 	 */
-	uv_convert_from_secure_pte(res);
+	WARN_ON_ONCE(uv_convert_from_secure_pte(res));
 	return res;
 }
 
-- 
2.52.0