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

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Message-ID: <14053472.RDIVbhacDa@gongov>
Date: Fri, 04 Oct 2024 12:36:09 +0200
From: Niels Dettenbach <nd@...dicat.com>
To: x86@...nel.org, Borislav Petkov <bp@...en8.de>,
 Jürgen Groß <jgross@...e.com>
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

Am Freitag, 4. Oktober 2024, 12:29:57  schrieben Sie:
> 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.

Thanks Jürgen - will try until monday...

niels.

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