projects / mirror_edk2.git / blame
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|---|---|---|
| a24fbd60 MB |
1 | /** @file\r |
| 2 | Handle raising and lowering TPL from within nested interrupt handlers.\r | |
| 3 | \r | |
| 4 | Allows interrupt handlers to safely raise and lower the TPL to\r | |
| 5 | dispatch event notifications, correctly allowing for nested\r | |
| 6 | interrupts to occur without risking stack exhaustion.\r | |
| 7 | \r | |
| 8 | Copyright (C) 2022, Fen Systems Ltd.\r | |
| 9 | \r | |
| 10 | SPDX-License-Identifier: BSD-2-Clause-Patent\r | |
| 11 | **/\r | |
| 12 | \r | |
| 13 | #ifndef __NESTED_INTERRUPT_TPL_LIB__\r | |
| 14 | #define __NESTED_INTERRUPT_TPL_LIB__\r | |
| 15 | \r | |
| 16 | #include <Uefi/UefiBaseType.h>\r | |
| 17 | #include <Uefi/UefiSpec.h>\r | |
| 18 | #include <Protocol/DebugSupport.h>\r | |
| 19 | \r | |
| 20 | ///\r | |
| 21 | /// State shared between all invocations of a nested interrupt handler.\r | |
| 22 | ///\r | |
| 23 | typedef struct {\r | |
| 24 | ///\r | |
| 25 | /// Highest TPL that is currently the target of a call to\r | |
| 26 | /// RestoreTPL() by an instance of this interrupt handler.\r | |
| 27 | ///\r | |
| 28 | EFI_TPL InProgressRestoreTPL;\r | |
| 29 | ///\r | |
| 30 | /// Flag used to defer a call to RestoreTPL() from an inner instance\r | |
| 31 | /// of the interrupt handler to an outer instance of the same\r | |
| 32 | /// interrupt handler.\r | |
| 33 | ///\r | |
| 34 | BOOLEAN DeferredRestoreTPL;\r | |
| 35 | } NESTED_INTERRUPT_STATE;\r | |
| 36 | \r | |
| 37 | /**\r | |
| 38 | Raise the task priority level to TPL_HIGH_LEVEL.\r | |
| 39 | \r | |
| 40 | @param None.\r | |
| 41 | \r | |
| 42 | @return The task priority level at which the interrupt occurred.\r | |
| 43 | **/\r | |
| 44 | EFI_TPL\r | |
| 45 | EFIAPI\r | |
| 46 | NestedInterruptRaiseTPL (\r | |
| 47 | VOID\r | |
| 48 | );\r | |
| 49 | \r | |
| 50 | /**\r | |
| 51 | Lower the task priority back to the value at which the interrupt\r | |
| 52 | occurred.\r | |
| 53 | \r | |
| 54 | This is unfortunately messy. UEFI requires us to support nested\r | |
| 55 | interrupts, but provides no way for an interrupt handler to call\r | |
| 56 | RestoreTPL() without implicitly re-enabling interrupts. In a\r | |
| 57 | virtual machine, it is possible for a large burst of interrupts to\r | |
| 58 | arrive. We must prevent such a burst from leading to stack\r | |
| 59 | exhaustion, while continuing to allow nested interrupts to occur.\r | |
| 60 | \r | |
| 61 | Since nested interrupts are permitted, an interrupt handler may be\r | |
| 62 | invoked as an inner interrupt handler while an outer instance of the\r | |
| 63 | same interrupt handler is still inside its call to RestoreTPL().\r | |
| 64 | \r | |
| 65 | To avoid stack exhaustion, this call may therefore (when provably\r | |
| 66 | safe to do so) defer the actual TPL lowering to be performed by an\r | |
| 67 | outer instance of the same interrupt handler.\r | |
| 68 | \r | |
| 69 | @param InterruptedTPL The task priority level at which the interrupt\r | |
| 70 | occurred, as previously returned from\r | |
| 71 | NestedInterruptRaiseTPL().\r | |
| 72 | \r | |
| 73 | @param SystemContext A pointer to the system context when the\r | |
| 74 | interrupt occurred.\r | |
| 75 | \r | |
| 76 | @param IsrState A pointer to the state shared between all\r | |
| 77 | invocations of the nested interrupt handler.\r | |
| 78 | **/\r | |
| 79 | VOID\r | |
| 80 | EFIAPI\r | |
| 81 | NestedInterruptRestoreTPL (\r | |
| 82 | IN EFI_TPL InterruptedTPL,\r | |
| 83 | IN OUT EFI_SYSTEM_CONTEXT SystemContext,\r | |
| 84 | IN OUT NESTED_INTERRUPT_STATE *IsrState\r | |
| 85 | );\r | |
| 86 | \r | |
| 87 | #endif // __NESTED_INTERRUPT_TPL_LIB__\r |