/** @file | |
Handle raising and lowering TPL from within nested interrupt handlers. | |
Allows interrupt handlers to safely raise and lower the TPL to | |
dispatch event notifications, correctly allowing for nested | |
interrupts to occur without risking stack exhaustion. | |
Copyright (C) 2022, Fen Systems Ltd. | |
SPDX-License-Identifier: BSD-2-Clause-Patent | |
**/ | |
#ifndef __NESTED_INTERRUPT_TPL_LIB__ | |
#define __NESTED_INTERRUPT_TPL_LIB__ | |
#include <Uefi/UefiBaseType.h> | |
#include <Uefi/UefiSpec.h> | |
#include <Protocol/DebugSupport.h> | |
/// | |
/// State shared between all invocations of a nested interrupt handler. | |
/// | |
typedef struct { | |
/// | |
/// Highest TPL that is currently the target of a call to | |
/// RestoreTPL() by an instance of this interrupt handler. | |
/// | |
EFI_TPL InProgressRestoreTPL; | |
/// | |
/// Flag used to defer a call to RestoreTPL() from an inner instance | |
/// of the interrupt handler to an outer instance of the same | |
/// interrupt handler. | |
/// | |
BOOLEAN DeferredRestoreTPL; | |
} NESTED_INTERRUPT_STATE; | |
/** | |
Raise the task priority level to TPL_HIGH_LEVEL. | |
@param None. | |
@return The task priority level at which the interrupt occurred. | |
**/ | |
EFI_TPL | |
EFIAPI | |
NestedInterruptRaiseTPL ( | |
VOID | |
); | |
/** | |
Lower the task priority back to the value at which the interrupt | |
occurred. | |
This is unfortunately messy. UEFI requires us to support nested | |
interrupts, but provides no way for an interrupt handler to call | |
RestoreTPL() without implicitly re-enabling interrupts. In a | |
virtual machine, it is possible for a large burst of interrupts to | |
arrive. We must prevent such a burst from leading to stack | |
exhaustion, while continuing to allow nested interrupts to occur. | |
Since nested interrupts are permitted, an interrupt handler may be | |
invoked as an inner interrupt handler while an outer instance of the | |
same interrupt handler is still inside its call to RestoreTPL(). | |
To avoid stack exhaustion, this call may therefore (when provably | |
safe to do so) defer the actual TPL lowering to be performed by an | |
outer instance of the same interrupt handler. | |
@param InterruptedTPL The task priority level at which the interrupt | |
occurred, as previously returned from | |
NestedInterruptRaiseTPL(). | |
@param SystemContext A pointer to the system context when the | |
interrupt occurred. | |
@param IsrState A pointer to the state shared between all | |
invocations of the nested interrupt handler. | |
**/ | |
VOID | |
EFIAPI | |
NestedInterruptRestoreTPL ( | |
IN EFI_TPL InterruptedTPL, | |
IN OUT EFI_SYSTEM_CONTEXT SystemContext, | |
IN OUT NESTED_INTERRUPT_STATE *IsrState | |
); | |
#endif // __NESTED_INTERRUPT_TPL_LIB__ |