linux-kernel - Re: [PATCH 1/1] x86: SMP broken on Xen PV DomU since 6.9

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Message-ID: <45f3a10c-8695-42cb-abb8-8c13ce1a476b@suse.com>
Date: Fri, 4 Oct 2024 12:29:57 +0200
From: Jürgen Groß <jgross@...e.com>
To: x86@...nel.org, Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin"
 <hpa@...or.com>, "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>,
 linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/1] x86: SMP broken on Xen PV DomU since 6.9

On 04.10.24 12:05, Niels Dettenbach wrote:
> Virtual machines under Xen Hypervisor (DomU) running in Xen PV mode use a
> special, nonstandard synthetized CPU topology which "just works" under
> kernels 6.9.x while newer kernels wrongly assuming a "crash kernel" and
> disable SMP (reducing to one CPU core) because the newer topology
> implementation produces a wrong error "[Firmware Bug]: APIC enumeration
> order not specification compliant" after new topology checks which are
> improper for Xen PV platform. As a result, the kernel disables SMP and
> activates just one CPU core within the PV DomU "VM" (DomU in PV mode).
> 
> The patch disables the regarding checks if it is running in Xen PV
> mode (only) and bring back SMP / all CPUs as in the past to such DomU
> VMs. The Xen subsystem takes care of the proper interaction between "guest"
> (DomU) and the "host" (Dom0).
> 
> Signed-off-by: Niels Dettenbach <nd@...dicat.com>

Does the attached patch instead of yours help?

Compile tested only.

Juergen

View attachment "0001-x86-xen-mark-boot-CPU-of-PV-guest-in-MSR_IA32_APICBA.patch" of type "text/x-patch" (1066 bytes)

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