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