On 1/23/24 16:31, Michael Brown wrote:
> At TPL_HIGH_LEVEL, CPU interrupts are disabled (as per the UEFI
> specification) and so we should never encounter a situation in which
> an interrupt occurs at TPL_HIGH_LEVEL.
>
> Restoring TPL to TPL_HIGH_LEVEL is always a no-op. Return immediately
> from NestedInterruptRestoreTPL(TPL_HIGH_LEVEL), so that we do not need
> to consider the effect of this possible invariant violation on the
> remainder of the logic.
>
> Signed-off-by: Michael Brown <mc...@ipxe.org>
> ---
> MdeModulePkg/Library/NestedInterruptTplLib/Tpl.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/MdeModulePkg/Library/NestedInterruptTplLib/Tpl.c
> b/MdeModulePkg/Library/NestedInterruptTplLib/Tpl.c
> index d56c12a44529..99af553ab189 100644
> --- a/MdeModulePkg/Library/NestedInterruptTplLib/Tpl.c
> +++ b/MdeModulePkg/Library/NestedInterruptTplLib/Tpl.c
> @@ -99,6 +99,19 @@ NestedInterruptRestoreTPL (
> EFI_TPL SavedInProgressRestoreTPL;
> BOOLEAN DeferredRestoreTPL;
>
> + //
> + // 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.
> + //
> + // Restoring TPL to TPL_HIGH_LEVEL is always a no-op. Return
> + // immediately so that we do not need to consider the effect of this
> + // possible invariant violation in the logic below.
> + //
> + if (InterruptedTPL >= TPL_HIGH_LEVEL) {
> + return;
> + }
> +
> //
> // If the TPL at which this interrupt occurred is equal to that of
> // the in-progress RestoreTPL() for an outer instance of the same
Feels like the handling logic might as well be "panic" here (except edk2
does not have a central panic API that's suitable for all platforms). I
probably missed the previous discussion that led to this patch. Either
way, it seems reasonable.
Acked-by: Laszlo Ersek <ler...@redhat.com>
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