On 03/12/21 07:26, Ankur Arora wrote:
> Call the CPU hot-eject handler if one is installed. The condition for
> installation is (PcdCpuMaxLogicalProcessorNumber > 1), and there's
> a hot-unplug request.
>
> The handler is called from SmmCpuFeaturesRendezvousExit(), which is
> in-turn called at the tail-end of SmiRendezvous() after the BSP has
> signalled an SMI exit via the "AllCpusInSync" loop.
>
> Cc: Laszlo Ersek <ler...@redhat.com>
> Cc: Jordan Justen <jordan.l.jus...@intel.com>
> Cc: Ard Biesheuvel <ard.biesheu...@arm.com>
> Cc: Igor Mammedov <imamm...@redhat.com>
> Cc: Boris Ostrovsky <boris.ostrov...@oracle.com>
> Cc: Aaron Young <aaron.yo...@oracle.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3132
> Signed-off-by: Ankur Arora <ankur.a.ar...@oracle.com>
> ---
>
> Notes:
> Addresses the following comments from v8:
>
> (1) Add a MemoryFence() before accessing mCpuHotEjctData->Handler
> (and comment to that effect.)
>
> .../Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c | 34
> ++++++++++++++++++++++
> 1 file changed, 34 insertions(+)
Reviewed-by: Laszlo Ersek <ler...@redhat.com>
Thanks
Laszlo
> diff --git a/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c
> b/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c
> index 5c025bc717c3..fdf2380974fa 100644
> --- a/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c
> +++ b/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c
> @@ -452,6 +452,40 @@ SmmCpuFeaturesRendezvousExit (
> IN UINTN CpuIndex
> )
> {
> + //
> + // We only call the Handler if CPU hot-eject is enabled
> + // (PcdCpuMaxLogicalProcessorNumber > 1), and hot-eject is needed
> + // in this SMI exit (otherwise mCpuHotEjectData->Handler is not armed.)
> + //
> +
> + if (mCpuHotEjectData != NULL) {
> + CPU_HOT_EJECT_HANDLER Handler;
> +
> + //
> + // As the comment above mentions, mCpuHotEjectData->Handler might be
> + // written to on the BSP as part of handling of the CPU-ejection.
> + //
> + // We know that any initial assignment to mCpuHotEjectData->Handler
> + // (on the BSP, in the CpuHotplugMmi() context) is ordered-before the
> + // load below, since it is guaranteed to happen before the
> + // control-dependency of the BSP's SMI exit signal -- by way of a store
> + // to AllCpusInSync (on the BSP, in BspHandler()) and the corresponding
> + // AllCpusInSync loop (on the APs, in SmiRendezvous()) which depends on
> + // that store.
> + //
> + // This guarantees that these pieces of code can never execute
> + // simultaneously. In addition, we ensure that the following load is
> + // ordered-after the AllCpusInSync loop by using a MemoryFence() with
> + // acquire semantics.
> + //
> + MemoryFence();
> +
> + Handler = mCpuHotEjectData->Handler;
> +
> + if (Handler != NULL) {
> + Handler (CpuIndex);
> + }
> + }
> }
>
> /**
>
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