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);
--
2.39.0
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