s390/mm: KVM: pv: when tearing down, try to destroy protected pages

When ptep_get_and_clear_full is called for a mm teardown, we will now
attempt to destroy the secure pages. This will be faster than export.

In case it was not a teardown, or if for some reason the destroy page
UVC failed, we try with an export page, like before.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
Link: https://lore.kernel.org/r/20220628135619.32410-11-imbrenda@linux.ibm.com
Message-Id: <20220628135619.32410-11-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index f16403ba81ec915136c8e9a68c4022e41fc8397b..cf81acf3879c4d9069cd7a5b927ac6e5950cb20c 100644 (file)
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1182,9 +1182,22 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
        } else {
                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_owned_from_secure(pte_val(res) & PAGE_MASK);
+       /* Nothing to do */
+       if (!mm_is_protected(mm) || !pte_present(res))
+               return res;
+       /*
+        * At this point the reference through the mapping is still present.
+        * The notifier should have destroyed all protected vCPUs at this
+        * point, so the destroy should be successful.
+        */
+       if (full && !uv_destroy_owned_page(pte_val(res) & PAGE_MASK))
+               return res;
+       /*
+        * 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.
+        */
+       uv_convert_owned_from_secure(pte_val(res) & PAGE_MASK);
        return res;
 }