On 1/18/23 14:10, Gerd Hoffmann wrote:
> Hi,
>
>> ... you could introduce a new fw_cfg boolean switch (and explain it in
>> the hang message) that meant: "I know what this QEMU bug is, I
>> understand its consequences are obscure, risky, and far-reaching in
>> OVMF, I've been warned, I know what I'm doing". That's a relatively
>> small addition to this patch, and then the risk is assumed by the user.
>> It resolves "being out of luck *entirely*".
>
> Using -fw_cfg would work on old qemu versions indeed.
>
> take care,
> Gerd
>
> From 65a4f683eaf94f82693811ce9b2393586a15afd7 Mon Sep 17 00:00:00 2001
> From: Gerd Hoffmann <kra...@redhat.com>
> Date: Fri, 13 Jan 2023 13:07:36 +0100
> Subject: [PATCH 1/1] OvmfPkg/PlatformInitLib: add switch to disable cpu
> hotplug support.
>
> Add a fw_cfg-based switch to disable cpu hotplug support in OVMF.
> This allows to boot OVMF on known-broken qemu versions.
>
> This is only safe to do in case hotplug is not used. Taking care
> of that is left to the user.
>
> Signed-off-by: Gerd Hoffmann <kra...@redhat.com>
> ---
> OvmfPkg/Library/PlatformInitLib/Platform.c | 30 ++++++++++++++++++++--
> 1 file changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/OvmfPkg/Library/PlatformInitLib/Platform.c
> b/OvmfPkg/Library/PlatformInitLib/Platform.c
> index c3d5f5eeb375..15811a4ff726 100644
> --- a/OvmfPkg/Library/PlatformInitLib/Platform.c
> +++ b/OvmfPkg/Library/PlatformInitLib/Platform.c
> @@ -414,8 +414,12 @@ PlatformMaxCpuCountInitialization (
> IN OUT EFI_HOB_PLATFORM_INFO *PlatformInfoHob
> )
> {
> - UINT16 BootCpuCount = 0;
> - UINT32 MaxCpuCount;
> + FIRMWARE_CONFIG_ITEM SupportedFeaturesItem;
> + UINTN SupportedFeaturesSize;
> + EFI_STATUS Status;
> + UINT16 BootCpuCount = 0;
> + UINT32 MaxCpuCount;
> + BOOLEAN CpuHotplugDisabled = FALSE;
>
> //
> // Try to fetch the boot CPU count.
> @@ -425,6 +429,15 @@ PlatformMaxCpuCountInitialization (
> BootCpuCount = QemuFwCfgRead16 ();
> }
>
> + Status = QemuFwCfgFindFile (
> + "opt/org.tianocore/nocpuhotplug",
> + &SupportedFeaturesItem,
> + &SupportedFeaturesSize
> + );
> + if (!EFI_ERROR (Status)) {
> + CpuHotplugDisabled = TRUE;
> + }
> +
> if (BootCpuCount == 0) {
> //
> // QEMU doesn't report the boot CPU count. (BootCpuCount == 0) will let
> @@ -434,6 +447,9 @@ PlatformMaxCpuCountInitialization (
> //
> DEBUG ((DEBUG_WARN, "%a: boot CPU count unavailable\n", __FUNCTION__));
> MaxCpuCount = PlatformInfoHob->DefaultMaxCpuNumber;
> + } else if (CpuHotplugDisabled) {
> + DEBUG ((DEBUG_INFO, "%a: CPU hotplug support disabled via
> opt/org.tianocore/nocpuhotplug\n", __FUNCTION__));
> + MaxCpuCount = BootCpuCount;
> } else {
> //
> // We will expose BootCpuCount to MpInitLib. MpInitLib will count APs up
> to
> @@ -563,12 +579,22 @@ PlatformMaxCpuCountInitialization (
> DEBUG_ERROR,
> "%a: Broken CPU hotplug register block: Present=%u Possible=%u.\n"
> "%a: Update QEMU to v8, or to stable with dab30fbef389
> backported.\n"
> + "\n"
> + "%a: Alternatively start qemu with:\n"
> + "%a: -fw_cfg name=opt/org.tianocore/nocpuhotplug,string=1\n"
> + "%a: to disable OVMF cpu hotplug support. Note that you must\n"
> + "%a: not ask qemu to hotplug CPUs then\n"
> + "\n"
> "%a: Refer to "
> "<https://bugzilla.tianocore.org/show_bug.cgi?id=4250>.\n",
> __FUNCTION__,
> Present,
> Possible,
> __FUNCTION__,
> + __FUNCTION__,
> + __FUNCTION__,
> + __FUNCTION__,
> + __FUNCTION__,
> __FUNCTION__
> ));
> ASSERT (FALSE);
... let me post a v3 in this direction, later.
Thanks
Laszlo
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