On 03/12/21 07:26, Ankur Arora wrote:
> @@ -214,6 +243,83 @@ EjectCpu (
> {
> UINT64 QemuSelector;
>
> + if (CheckIfBsp ()) {
> + UINT32 Idx;
> +
> + for (Idx = 0; Idx < mCpuHotEjectData->ArrayLength; Idx++) {
> + UINT64 QemuSelector;
Visual Studio warns that the inner QemuSelector declaration shadows the
outer one. I'm going to remove the inner declaration, due to:
> +
> + QemuSelector = mCpuHotEjectData->QemuSelectorMap[Idx];
> +
> + if (QemuSelector != CPU_EJECT_QEMU_SELECTOR_INVALID) {
> + //
> + // This to-be-ejected-CPU has already received the BSP's SMI exit
> + // signal and will execute SmmCpuFeaturesRendezvousExit()
> + // followed by this callback or is already penned in the
> + // CpuSleep() loop below.
> + //
> + // Tell QEMU to context-switch it out.
> + //
> + QemuCpuhpWriteCpuSelector (mMmCpuIo, (UINT32) QemuSelector);
> + QemuCpuhpWriteCpuStatus (mMmCpuIo, QEMU_CPUHP_STAT_EJECT);
> +
> + //
> + // Now that we've ejected the CPU corresponding to
> QemuSelectorMap[Idx],
> + // clear its eject status to ensure that an invalid future SMI does
> + // not end up trying a spurious eject or a newly hotplugged CPU does
> + // not get penned in the CpuSleep() loop.
> + //
> + // Note that the QemuCpuhpWriteCpuStatus() command above is a write
> to
> + // a different address space and uses the EFI_MM_CPU_IO_PROTOCOL.
> + //
> + // This means that we are guaranteed that the following assignment
> + // will not be reordered before the eject. And, so we can safely
> + // do this write here.
> + //
> + mCpuHotEjectData->QemuSelectorMap[Idx] =
> + CPU_EJECT_QEMU_SELECTOR_INVALID;
> +
> + DEBUG ((DEBUG_INFO, "%a: Unplugged ProcessorNum %u, "
> + "QemuSelector %Lu\n", __FUNCTION__, Idx, QemuSelector));
> + }
> + }
> +
> + //
> + // We are done until the next hot-unplug; clear the handler.
> + //
> + // mCpuHotEjectData->Handler is a NOP for any CPU not under ejection.
> + // So, once we are done with all the ejections, we can safely reset it
> + // here since any CPU dereferencing it would only see either the old
> + // or the new value (since it is aligned at a natural boundary.)
> + //
> + mCpuHotEjectData->Handler = NULL;
> + return;
> + }
> +
> + //
> + // Reached only on APs
> + //
> +
> + //
> + // mCpuHotEjectData->QemuSelectorMap[ProcessorNum] is updated
> + // on the BSP in the ongoing SMI at two places:
> + //
> + // - UnplugCpus() where the BSP determines if a CPU is under ejection
> + // or not. As a comment in UnplugCpus() at set-up, and in
> + // SmmCpuFeaturesRendezvousExit() where it is dereferenced describe,
> + // any such updates are guaranteed to be ordered-before the
> + // dereference below.
> + //
> + // - EjectCpu() on the BSP (above) updates QemuSelectorMap[ProcessorNum]
> + // for a CPU once it's ejected.
> + //
> + // The CPU under ejection: might be executing anywhere between the
> + // AllCpusInSync loop in SmiRendezvous(), to about to dereference
> + // QemuSelectorMap[ProcessorNum].
> + // As described in the comment above where we do the reset, this
> + // is not a problem since the ejected CPU never sees the after value.
> + // CPUs not-under ejection: never see any changes so they are fine.
> + //
> QemuSelector = mCpuHotEjectData->QemuSelectorMap[ProcessorNum];
this reference being to the outer one.
Thanks
Laszlo
> if (QemuSelector == CPU_EJECT_QEMU_SELECTOR_INVALID) {
> return;
> @@ -495,11 +601,6 @@ CpuHotplugMmi (
> if (EFI_ERROR (Status)) {
> goto Fatal;
> }
> - if (ToUnplugCount > 0) {
> - DEBUG ((DEBUG_ERROR, "%a: hot-unplug is not supported yet\n",
> - __FUNCTION__));
> - goto Fatal;
> - }
>
> if (PluggedCount > 0) {
> Status = ProcessHotAddedCpus (mPluggedApicIds, PluggedCount);
>
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