On Fri, 13 Jan 2023 at 13:22, Gerd Hoffmann <kra...@redhat.com> wrote:
>
> On Fri, Jan 13, 2023 at 11:10:54AM +0100, Laszlo Ersek wrote:
> > On 1/13/23 10:32, Gerd Hoffmann wrote:
> > > On Fri, Jan 13, 2023 at 07:03:54AM +0100, Gerd Hoffmann wrote:
> > >> Hi,
> > >>
> > >>> - QEMU can be configured with other compat properties on the command
> > >>> line so that "CPU hotplug with SMI" and "CPU hot-unplug with SMI" *not*
> > >>> be offered to the firmware. Then QEMU will reject hotplug attempts, and
> > >>> the SMM hotplug code in edk2 will not be triggered by the (virtual)
> > >>> hardware.
> > >>
> > >> Can we have edk2 print instructions for that in the error message?
> > >
> > > This seems to be:
> > >
> > > qemu -M q35 \
> > > -global ICH9-LPC.x-smi-cpu-hotplug=off \
> > > -global ICH9-LPC.x-smi-cpu-hotunplug=off
> >
> > Yes, those are the flags.
> >
> > > But it appears to not work.
> >
> > They should work, but they take effect in QEMU, and not in the firmware.
> > These knobs control what CPU hot(un)plug+SMI features QEMU exposes to
> > the guest fw, via fw_cfg,
>
> Ok, I see, only the SMM code actually checks that.
>
> > In particular the firmware makes no further decisions based on whether
> > QEMU advertized some of these features.
>
> I was thinking the other way around: When cpu hotplug is disabled in
> qemu it should be safe to skip the whole cpu hotplug checking dance.
> See test patch below.
>
> That would give us a config switch (turn off cpu hotplug support) which
> would allow edk2 run on qemu versions with broken cpu hotplug.
>
> Does the idea look sane or do I miss something?
>
I cannot review the actual patch due to lack of x86/smm/qemu/hotplug
knowledge, but if this allows us to merge Laszlo's fix without
breaking all current QEMU/x86 TCG users, I'm all for it.
>
> commit bd2e36eba35268ab46c0125d2b9125391ea6f9fc
> Author: Gerd Hoffmann <kra...@redhat.com>
> Date: Fri Jan 13 13:07:36 2023 +0100
>
> skip cpu present checking when hotplug is off
>
> diff --git a/OvmfPkg/Library/PlatformInitLib/Platform.c
> b/OvmfPkg/Library/PlatformInitLib/Platform.c
> index 13348afb4890..2b0f0c836f85 100644
> --- a/OvmfPkg/Library/PlatformInitLib/Platform.c
> +++ b/OvmfPkg/Library/PlatformInitLib/Platform.c
> @@ -415,8 +415,9 @@ PlatformMaxCpuCountInitialization (
> IN OUT EFI_HOB_PLATFORM_INFO *PlatformInfoHob
> )
> {
> - UINT16 BootCpuCount = 0;
> - UINT32 MaxCpuCount;
> + UINT16 BootCpuCount = 0;
> + UINT32 MaxCpuCount;
> + BOOLEAN CpuHotplugSupported = FALSE;
>
> //
> // Try to fetch the boot CPU count.
> @@ -424,6 +425,31 @@ PlatformMaxCpuCountInitialization (
> if (QemuFwCfgIsAvailable ()) {
> QemuFwCfgSelectItem (QemuFwCfgItemSmpCpuCount);
> BootCpuCount = QemuFwCfgRead16 ();
> + DEBUG ((DEBUG_INFO, "%a: BootCpuCount: %d\n", __FUNCTION__,
> BootCpuCount));
> + }
> +
> + {
> + FIRMWARE_CONFIG_ITEM SupportedFeaturesItem;
> + UINTN SupportedFeaturesSize;
> + UINT64 mSmiFeatures;
> + EFI_STATUS Status;
> +
> + Status = QemuFwCfgFindFile (
> + "etc/smi/supported-features",
> + &SupportedFeaturesItem,
> + &SupportedFeaturesSize
> + );
> +
> + if (EFI_ERROR (Status)) {
> + DEBUG ((DEBUG_INFO, "%a: etc/smi/supported-features: %r\n",
> __FUNCTION__, Status));
> + } else {
> + QemuFwCfgSelectItem (SupportedFeaturesItem);
> + QemuFwCfgReadBytes (sizeof mSmiFeatures, &mSmiFeatures);
> + DEBUG ((DEBUG_INFO, "%a: etc/smi/supported-features: 0x%x\n",
> __FUNCTION__, mSmiFeatures));
> + if (mSmiFeatures & (BIT1 /* hotplug */ | BIT2 /* hotunplug */)) {
> + CpuHotplugSupported = TRUE;
> + }
> + }
> }
>
> if (BootCpuCount == 0) {
> @@ -435,6 +461,9 @@ PlatformMaxCpuCountInitialization (
> //
> DEBUG ((DEBUG_WARN, "%a: boot CPU count unavailable\n", __FUNCTION__));
> MaxCpuCount = PlatformInfoHob->DefaultMaxCpuNumber;
> + } else if (!CpuHotplugSupported) {
> + DEBUG ((DEBUG_INFO, "%a: CPU hotplug support not available\n",
> __FUNCTION__));
> + MaxCpuCount = BootCpuCount;
> } else {
> //
> // We will expose BootCpuCount to MpInitLib. MpInitLib will count APs up
> to
>
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