[PATCH v14 4/6] KVM: s390: pv: avoid export before import if possible

Claudio Imbrenda
2022-09-30T14:02:10Z

If the appropriate UV feature bit is set, there is no need to perform
an export before import.

The misc feature indicates, among other things, that importing a shared
page from a different protected VM will automatically also transfer its
ownership.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Nico Boehr <nrb@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
---
arch/s390/kernel/uv.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index f9810d2a267c..9f18a4af9c13 100644
--- a/arch/s390/kernel/uv.c
+++ b/arch/s390/kernel/uv.c
@@ -255,6 +255,13 @@ static int make_secure_pte(pte_t *ptep, unsigned long addr,
*/
static bool should_export_before_import(struct uv_cb_header *uvcb, struct mm_struct *mm)
{
+ /*
+ * The misc feature indicates, among other things, that importing a
+ * shared page from a different protected VM will automatically also
+ * transfer its ownership.
+ */
+ if (test_bit_inv(BIT_UV_FEAT_MISC, &uv_info.uv_feature_indications))
+ return false;
if (uvcb->cmd == UVC_CMD_UNPIN_PAGE_SHARED)
return false;
return atomic_read(&mm->context.protected_count) > 1;
--
2.37.3