[PATCH] efi: pstore: Support late setup with TEE-backed efivars ops

[Val Packett <val@packett.cool>]

On some platforms, EFI variable services only become available when an
appropriate TEE driver is initialized such as qseecom, gsmi or stmm.

This would work fine when efi_pstore was built as a module and loaded
late by userspace, but with CONFIG_EFI_VARS_PSTORE=y this driver would
quit due to non-writable efivars before the necessary driver had any
chance to load.

Listen to efivar_ops_nh notifications and retry the initialization when
writable EFI variable ops become available.

Signed-off-by: Val Packett <val@packett.cool>
---
 drivers/firmware/efi/efi-pstore.c | 32 +++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
index a253b6144945..ad5192d5892e 100644
--- a/drivers/firmware/efi/efi-pstore.c
+++ b/drivers/firmware/efi/efi-pstore.c
@@ -253,14 +253,11 @@ static struct pstore_info efi_pstore_info = {
 	.erase		= efi_pstore_erase,
 };
 
-static int efivars_pstore_init(void)
+static int efivars_pstore_setup(void)
 {
 	if (!efivar_supports_writes())
 		return 0;
 
-	if (pstore_disable)
-		return 0;
-
 	/*
 	 * Notice that 1024 is the minimum here to prevent issues with
 	 * decompression algorithms that were spotted during tests;
@@ -285,8 +282,35 @@ static int efivars_pstore_init(void)
 	return 0;
 }
 
+static int efivars_pstore_ops_notifier(struct notifier_block *nb,
+				 unsigned long event, void *data)
+{
+	if (event == EFIVAR_OPS_RDWR && !efi_pstore_info.bufsize)
+		efivars_pstore_setup();
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block efivars_pstore_ops_notifier_block = {
+	.notifier_call = efivars_pstore_ops_notifier,
+};
+
+static int efivars_pstore_init(void)
+{
+	if (pstore_disable)
+		return 0;
+
+	blocking_notifier_chain_register(&efivar_ops_nh,
+					&efivars_pstore_ops_notifier_block);
+
+	return efivars_pstore_setup();
+}
+
 static void efivars_pstore_exit(void)
 {
+	blocking_notifier_chain_unregister(&efivar_ops_nh,
+					&efivars_pstore_ops_notifier_block);
+
 	if (!efi_pstore_info.bufsize)
 		return;
 
-- 
2.51.0