[PATCH 3/3] efi: replace runtime services spinlock with semaphore

[Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>]

The purpose of the efi_runtime_lock is to prevent concurrent calls into
the firmware. There is no need to use spinlocks here, as long as we ensure
that runtime service invocations from an atomic context (i.e., EFI pstore)
cannot block.

So use a semaphore instead, and use down_trylock() in the nonblocking case.
We don't use a mutex here because the mutex_trylock() function must not
be called from interrupt context, whereas the down_trylock() can.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
---
 drivers/firmware/efi/runtime-wrappers.c | 77 +++++++++++---------
 include/linux/efi.h                     |  1 +
 2 files changed, 45 insertions(+), 33 deletions(-)

diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index de6953039af6..47278efd3ea6 100644
--- a/drivers/firmware/efi/runtime-wrappers.c
+++ b/drivers/firmware/efi/runtime-wrappers.c
@@ -16,8 +16,7 @@
 
 #include <linux/bug.h>
 #include <linux/efi.h>
-#include <linux/mutex.h>
-#include <linux/spinlock.h>
+#include <linux/semaphore.h>
 #include <asm/efi.h>
 
 /*
@@ -54,20 +53,21 @@
  * +------------------------------------+-------------------------------+
  *
  * Due to the fact that the EFI pstore may write to the variable store in
- * interrupt context, we need to use a spinlock for at least the groups that
+ * interrupt context, we need to use a lock for at least the groups that
  * contain SetVariable() and QueryVariableInfo(). That leaves little else, as
  * none of the remaining functions are actually ever called at runtime.
- * So let's just use a single spinlock to serialize all Runtime Services calls.
+ * So let's just use a single lock to serialize all Runtime Services calls.
  */
-static DEFINE_SPINLOCK(efi_runtime_lock);
+static DEFINE_SEMAPHORE(efi_runtime_lock);
 
 static efi_status_t virt_efi_get_time(efi_time_t *tm, efi_time_cap_t *tc)
 {
 	efi_status_t status;
 
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	status = efi_call_virt(get_time, tm, tc);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -75,9 +75,10 @@ static efi_status_t virt_efi_set_time(efi_time_t *tm)
 {
 	efi_status_t status;
 
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	status = efi_call_virt(set_time, tm);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -87,9 +88,10 @@ static efi_status_t virt_efi_get_wakeup_time(efi_bool_t *enabled,
 {
 	efi_status_t status;
 
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	status = efi_call_virt(get_wakeup_time, enabled, pending, tm);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -97,9 +99,10 @@ static efi_status_t virt_efi_set_wakeup_time(efi_bool_t enabled, efi_time_t *tm)
 {
 	efi_status_t status;
 
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	status = efi_call_virt(set_wakeup_time, enabled, tm);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -111,10 +114,11 @@ static efi_status_t virt_efi_get_variable(efi_char16_t *name,
 {
 	efi_status_t status;
 
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	status = efi_call_virt(get_variable, name, vendor, attr, data_size,
 			       data);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -124,9 +128,10 @@ static efi_status_t virt_efi_get_next_variable(unsigned long *name_size,
 {
 	efi_status_t status;
 
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	status = efi_call_virt(get_next_variable, name_size, name, vendor);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -138,10 +143,11 @@ static efi_status_t virt_efi_set_variable(efi_char16_t *name,
 {
 	efi_status_t status;
 
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	status = efi_call_virt(set_variable, name, vendor, attr, data_size,
 			       data);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -152,12 +158,12 @@ virt_efi_set_variable_nonblocking(efi_char16_t *name, efi_guid_t *vendor,
 {
 	efi_status_t status;
 
-	if (!spin_trylock(&efi_runtime_lock))
+	if (down_trylock(&efi_runtime_lock))
 		return EFI_NOT_READY;
 
 	status = efi_call_virt(set_variable, name, vendor, attr, data_size,
 			       data);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -172,10 +178,11 @@ static efi_status_t virt_efi_query_variable_info(u32 attr,
 	if (efi.runtime_version < EFI_2_00_SYSTEM_TABLE_REVISION)
 		return EFI_UNSUPPORTED;
 
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	status = efi_call_virt(query_variable_info, attr, storage_space,
 			       remaining_space, max_variable_size);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -190,12 +197,12 @@ virt_efi_query_variable_info_nonblocking(u32 attr,
 	if (efi.runtime_version < EFI_2_00_SYSTEM_TABLE_REVISION)
 		return EFI_UNSUPPORTED;
 
-	if (!spin_trylock(&efi_runtime_lock))
+	if (down_trylock(&efi_runtime_lock))
 		return EFI_NOT_READY;
 
 	status = efi_call_virt(query_variable_info, attr, storage_space,
 			       remaining_space, max_variable_size);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -203,9 +210,10 @@ static efi_status_t virt_efi_get_next_high_mono_count(u32 *count)
 {
 	efi_status_t status;
 
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	status = efi_call_virt(get_next_high_mono_count, count);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -214,9 +222,10 @@ static void virt_efi_reset_system(int reset_type,
 				  unsigned long data_size,
 				  efi_char16_t *data)
 {
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	__efi_call_virt(reset_system, reset_type, status, data_size, data);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 }
 
 static efi_status_t virt_efi_update_capsule(efi_capsule_header_t **capsules,
@@ -228,9 +237,10 @@ static efi_status_t virt_efi_update_capsule(efi_capsule_header_t **capsules,
 	if (efi.runtime_version < EFI_2_00_SYSTEM_TABLE_REVISION)
 		return EFI_UNSUPPORTED;
 
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	status = efi_call_virt(update_capsule, capsules, count, sg_list);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
@@ -244,10 +254,11 @@ static efi_status_t virt_efi_query_capsule_caps(efi_capsule_header_t **capsules,
 	if (efi.runtime_version < EFI_2_00_SYSTEM_TABLE_REVISION)
 		return EFI_UNSUPPORTED;
 
-	spin_lock(&efi_runtime_lock);
+	if (down_interruptible(&efi_runtime_lock))
+		return EFI_ABORTED;
 	status = efi_call_virt(query_capsule_caps, capsules, count, max_size,
 			       reset_type);
-	spin_unlock(&efi_runtime_lock);
+	up(&efi_runtime_lock);
 	return status;
 }
 
diff --git a/include/linux/efi.h b/include/linux/efi.h
index b088eae349b8..b2ac50266368 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -35,6 +35,7 @@
 #define EFI_WRITE_PROTECTED	( 8 | (1UL << (BITS_PER_LONG-1)))
 #define EFI_OUT_OF_RESOURCES	( 9 | (1UL << (BITS_PER_LONG-1)))
 #define EFI_NOT_FOUND		(14 | (1UL << (BITS_PER_LONG-1)))
+#define EFI_ABORTED		(21 | (1UL << (BITS_PER_LONG-1)))
 #define EFI_SECURITY_VIOLATION	(26 | (1UL << (BITS_PER_LONG-1)))
 
 typedef unsigned long efi_status_t;
-- 
2.5.0

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