pstore/pmsg: drop bounce buffer

Removing a bounce buffer copy operation in the pmsg driver path is
always better. We also gain in overall performance by not requesting
a vmalloc on every write as this can cause precious RT tasks, such
as user facing media operation, to stall while memory is being
reclaimed. Added a write_buf_user to the pstore functions, a backup
platform write_buf_user that uses the small buffer that is part of
the instance, and implemented a ramoops write_buf_user that only
supports PSTORE_TYPE_PMSG.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

fs/pstore/ram.c

@@ -331,6 +331,24 @@ static int notrace ramoops_pstore_write_buf(enum pstore_type_id type,
 	return 0;
 }
 
+static int notrace ramoops_pstore_write_buf_user(enum pstore_type_id type,
+						 enum kmsg_dump_reason reason,
+						 u64 *id, unsigned int part,
+						 const char __user *buf,
+						 bool compressed, size_t size,
+						 struct pstore_info *psi)
+{
+	if (type == PSTORE_TYPE_PMSG) {
+		struct ramoops_context *cxt = psi->data;
+
+		if (!cxt->mprz)
+			return -ENOMEM;
+		return persistent_ram_write_user(cxt->mprz, buf, size);
+	}
+
+	return -EINVAL;
+}
+
 static int ramoops_pstore_erase(enum pstore_type_id type, u64 id, int count,
 				struct timespec time, struct pstore_info *psi)
 {
@@ -369,6 +387,7 @@ static struct ramoops_context oops_cxt = {
 		.open	= ramoops_pstore_open,
 		.read	= ramoops_pstore_read,
 		.write_buf	= ramoops_pstore_write_buf,
+		.write_buf_user	= ramoops_pstore_write_buf_user,
 		.erase	= ramoops_pstore_erase,
 	},
 };