[PATCH v1 1/1] s390/uv: Prealloc and use one work page

[Harald Freudenberger <freude@linux.ibm.com>]

The pkey handler is calling the uv in some circumstances
where no memory allocation is acceptable. As of now only
the uv_get_secret_metadata() function allocates memory.
As this is exactly one page, lets introduce a pre-allocated
work page and protect the concurrent use with a mutex to
remove dynamic memory allocation and free. This page may be
also used with future extension to the uv code.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
---
 arch/s390/kernel/uv.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index 9f05df2da2f7..71900ec68a23 100644
--- a/arch/s390/kernel/uv.c
+++ b/arch/s390/kernel/uv.c
@@ -37,6 +37,13 @@ EXPORT_SYMBOL(uv_info);
 int __bootdata_preserved(prot_virt_host);
 EXPORT_SYMBOL(prot_virt_host);
 
+/*
+ * Need one work page for ephemeral use by uv_get_secret_metadata()
+ * The concurrent use of this page is protected by a mutex.
+ */
+static u8 *work_page;
+static DEFINE_MUTEX(work_page_lock);
+
 static int __init uv_init(phys_addr_t stor_base, unsigned long stor_len)
 {
 	struct uv_cb_init uvcb = {
@@ -61,6 +68,12 @@ void __init setup_uv(void)
 	if (!is_prot_virt_host())
 		return;
 
+	work_page = (u8 *)__get_free_page(GFP_KERNEL);
+	if (!work_page) {
+		pr_warn("Failed to alloc a working memory page\n");
+		return;
+	}
+
 	uv_stor_base = memblock_alloc_try_nid(
 		uv_info.uv_base_stor_len, SZ_1M, SZ_2G,
 		MEMBLOCK_ALLOC_ACCESSIBLE, NUMA_NO_NODE);
@@ -80,6 +93,7 @@ void __init setup_uv(void)
 	return;
 fail:
 	pr_info("Disabling support for protected virtualization");
+	free_page((unsigned long)work_page);
 	prot_virt_host = 0;
 }
 
@@ -730,11 +744,11 @@ int uv_get_secret_metadata(const u8 secret_id[UV_SECRET_ID_LEN],
 	struct uv_secret_list *buf;
 	int rc;
 
-	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
+	mutex_lock(&work_page_lock);
+	buf = (struct uv_secret_list *)work_page;
 	rc = find_secret(secret_id, buf, secret);
-	kfree(buf);
+	mutex_unlock(&work_page_lock);
+
 	return rc;
 }
 EXPORT_SYMBOL_GPL(uv_get_secret_metadata);
-- 
2.43.0