apologies, I've got more comments here:
On 01/29/21 01:59, Ankur Arora wrote:
> /**
> + CPU Hot-eject handler, called from SmmCpuFeaturesRendezvousExit(),
> + on each CPU at exit from SMM.
> +
> + If, the executing CPU is not being ejected, nothing to be done.
> + If, the executing CPU is being ejected, wait in a CpuDeadLoop()
> + until ejected.
> +
> + @param[in] ProcessorNum Index of executing CPU.
> +
> +**/
> +VOID
> +EFIAPI
> +CpuEject (
> + IN UINTN ProcessorNum
> + )
> +{
> + //
> + // APIC ID is UINT32, but mCpuHotEjectData->ApicIdMap[] is UINT64
> + // so use UINT64 throughout.
> + //
> + UINT64 ApicId;
> +
> + ApicId = mCpuHotEjectData->ApicIdMap[ProcessorNum];
> + if (ApicId == CPU_EJECT_INVALID) {
> + return;
> + }
> +
> + //
> + // CPU(s) being unplugged get here from SmmCpuFeaturesSmiRendezvousExit()
> + // after having been cleared to exit the SMI by the monarch and thus have
> + // no SMM processing remaining.
> + //
> + // Given that we cannot allow them to escape to the guest, we pen them
> + // here until the SMM monarch tells the HW to unplug them.
> + //
> + CpuDeadLoop ();
> +}
(15) There is no such function as SmmCpuFeaturesSmiRendezvousExit() --
it's SmmCpuFeaturesRendezvousExit().
(16) This function uses a data structure for communication between BSP
and APs -- mCpuHotEjectData->ApicIdMap is modified in UnplugCpus() on
the BSP, and checked above by the APs (too).
What guarantees the visibility of mCpuHotEjectData->ApicIdMap?
I think we might want to use InterlockedCompareExchange64() in both
EjectCpu() and UnplugCpus() (and make "ApicIdMap" volatile, in
addition). InterlockedCompareExchange64() can be used just for
comparison as well, by passing ExchangeValue=CompareValue.
(17) I think a similar observation applies to the "Handler" field too,
as APs call it, while the BSP keeps flipping it between NULL and a real
function address. We might have to turn that field into an
EFI_PHYSICAL_ADDRESS (just a fancy name for UINT64), and use
InterlockedCompareExchange64() again.
Thanks
Laszlo
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