diff options
| -rw-r--r-- | OvmfPkg/Library/NestedInterruptTplLib/Tpl.c | 21 |
1 files changed, 18 insertions, 3 deletions
diff --git a/OvmfPkg/Library/NestedInterruptTplLib/Tpl.c b/OvmfPkg/Library/NestedInterruptTplLib/Tpl.c index e921a09c55..d56c12a445 100644 --- a/OvmfPkg/Library/NestedInterruptTplLib/Tpl.c +++ b/OvmfPkg/Library/NestedInterruptTplLib/Tpl.c @@ -34,12 +34,27 @@ NestedInterruptRaiseTPL ( //
// Raise TPL and assert that we were called from within an interrupt
- // handler (i.e. with TPL below TPL_HIGH_LEVEL but with interrupts
- // disabled).
+ // handler (i.e. with interrupts already disabled before raising the
+ // TPL).
//
ASSERT (GetInterruptState () == FALSE);
InterruptedTPL = gBS->RaiseTPL (TPL_HIGH_LEVEL);
- ASSERT (InterruptedTPL < TPL_HIGH_LEVEL);
+
+ //
+ // At TPL_HIGH_LEVEL, CPU interrupts are disabled (as per the UEFI
+ // specification) and so we should never encounter a situation in
+ // which InterruptedTPL==TPL_HIGH_LEVEL. The specification also
+ // restricts usage of TPL_HIGH_LEVEL to the firmware itself.
+ //
+ // However, nothing actually prevents a UEFI application from
+ // invalidly calling gBS->RaiseTPL(TPL_HIGH_LEVEL) and then
+ // violating the invariant by enabling interrupts via the STI or
+ // equivalent instruction. Some versions of the Microsoft Windows
+ // bootloader are known to do this.
+ //
+ if (InterruptedTPL >= TPL_HIGH_LEVEL) {
+ DEBUG ((DEBUG_ERROR, "ERROR: Interrupts enabled at TPL_HIGH_LEVEL!\n"));
+ }
return InterruptedTPL;
}
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