3 files changed, 72 insertions, 0 deletions

diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index 9694cba665c4..4349206198b2 100644
--- a/drivers/firmware/efi/runtime-wrappers.c
+++ b/drivers/firmware/efi/runtime-wrappers.c
@@ -200,6 +200,24 @@ static efi_status_t virt_efi_set_variable(efi_char16_t *name,
         return status;
 }
 
+static efi_status_t
+virt_efi_set_variable_nonblocking(efi_char16_t *name, efi_guid_t *vendor,
+                                  u32 attr, unsigned long data_size,
+                                  void *data)
+{
+        unsigned long flags;
+        efi_status_t status;
+
+        if (!spin_trylock_irqsave(&efi_runtime_lock, flags))
+                return EFI_NOT_READY;
+
+        status = efi_call_virt(set_variable, name, vendor, attr, data_size,
+                               data);
+        spin_unlock_irqrestore(&efi_runtime_lock, flags);
+        return status;
+}
+
+
 static efi_status_t virt_efi_query_variable_info(u32 attr,
                                                  u64 *storage_space,
                                                  u64 *remaining_space,
@@ -287,6 +305,7 @@ void efi_native_runtime_setup(void)
         efi.get_variable = virt_efi_get_variable;
         efi.get_next_variable = virt_efi_get_next_variable;
         efi.set_variable = virt_efi_set_variable;
+        efi.set_variable_nonblocking = virt_efi_set_variable_nonblocking;
         efi.get_next_high_mono_count = virt_efi_get_next_high_mono_count;
         efi.reset_system = virt_efi_reset_system;
         efi.query_variable_info = virt_efi_query_variable_info;
diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 1fa724f31b0e..fa3c66bdc1e5 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -595,6 +595,39 @@ int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
 }
 EXPORT_SYMBOL_GPL(efivar_entry_set);
 
+/*
+ * efivar_entry_set_nonblocking - call set_variable_nonblocking()
+ *
+ * This function is guaranteed to not block and is suitable for calling
+ * from crash/panic handlers.
+ *
+ * Crucially, this function will not block if it cannot acquire
+ * __efivars->lock. Instead, it returns -EBUSY.
+ */
+static int
+efivar_entry_set_nonblocking(efi_char16_t *name, efi_guid_t vendor,
+                             u32 attributes, unsigned long size, void *data)
+{
+        const struct efivar_operations *ops = __efivars->ops;
+        unsigned long flags;
+        efi_status_t status;
+
+        if (!spin_trylock_irqsave(&__efivars->lock, flags))
+                return -EBUSY;
+
+        status = check_var_size(attributes, size + ucs2_strsize(name, 1024));
+        if (status != EFI_SUCCESS) {
+                spin_unlock_irqrestore(&__efivars->lock, flags);
+                return -ENOSPC;
+        }
+
+        status = ops->set_variable_nonblocking(name, &vendor, attributes,
+                                               size, data);
+
+        spin_unlock_irqrestore(&__efivars->lock, flags);
+        return efi_status_to_err(status);
+}
+
 /**
  * efivar_entry_set_safe - call set_variable() if enough space in firmware
  * @name: buffer containing the variable name
@@ -622,6 +655,20 @@ int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
         if (!ops->query_variable_store)
                 return -ENOSYS;
 
+        /*
+         * If the EFI variable backend provides a non-blocking
+         * ->set_variable() operation and we're in a context where we
+         * cannot block, then we need to use it to avoid live-locks,
+         * since the implication is that the regular ->set_variable()
+         * will block.
+         *
+         * If no ->set_variable_nonblocking() is provided then
+         * ->set_variable() is assumed to be non-blocking.
+         */
+        if (!block && ops->set_variable_nonblocking)
+                return efivar_entry_set_nonblocking(name, vendor, attributes,
+                                                    size, data);
+
         if (!block) {
                 if (!spin_trylock_irqsave(&__efivars->lock, flags))
                         return -EBUSY;
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 78b29b133e14..0949f9c7e872 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -503,6 +503,10 @@ typedef efi_status_t efi_get_next_variable_t (unsigned long *name_size, efi_char
 typedef efi_status_t efi_set_variable_t (efi_char16_t *name, efi_guid_t *vendor, 
                                          u32 attr, unsigned long data_size,
                                          void *data);
+typedef efi_status_t
+efi_set_variable_nonblocking_t(efi_char16_t *name, efi_guid_t *vendor,
+                               u32 attr, unsigned long data_size, void *data);
+
 typedef efi_status_t efi_get_next_high_mono_count_t (u32 *count);
 typedef void efi_reset_system_t (int reset_type, efi_status_t status,
                                  unsigned long data_size, efi_char16_t *data);
@@ -822,6 +826,7 @@ extern struct efi {
         efi_get_variable_t *get_variable;
         efi_get_next_variable_t *get_next_variable;
         efi_set_variable_t *set_variable;
+        efi_set_variable_nonblocking_t *set_variable_nonblocking;
         efi_query_variable_info_t *query_variable_info;
         efi_update_capsule_t *update_capsule;
         efi_query_capsule_caps_t *query_capsule_caps;
@@ -1042,6 +1047,7 @@ struct efivar_operations {
         efi_get_variable_t *get_variable;
         efi_get_next_variable_t *get_next_variable;
         efi_set_variable_t *set_variable;
+        efi_set_variable_nonblocking_t *set_variable_nonblocking;
         efi_query_variable_store_t *query_variable_store;
 };