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

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Message-ID: <3635258.LM0AJKV5NW@gongov>
Date: Mon, 07 Oct 2024 12:29:46 +0200
From: Niels Dettenbach <nd@...dicat.com>
To: x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc: Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.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,
 xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 1/1] x86: SMP broken on Xen PV DomU since 6.9

Am Freitag, 4. Oktober 2024, 12:29:57  schrieb Jürgen Groß:
> 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.


it does ß)))


domU:
-- snip --
vcpus=6
cpu="12,13,14,15,23,24"
-- snap --


-- snip --
[    0.500458] cpu 0 spinlock event irq 1
[    0.500485] VPMU disabled by hypervisor.
[    0.501273] Performance Events: unsupported p6 CPU model 62 no PMU driver, software events only.
[    0.501304] signal: max sigframe size: 1776
[    0.501410] rcu: Hierarchical SRCU implementation.
[    0.501428] rcu:     Max phase no-delay instances is 400.
[    0.502032] NMI watchdog: Perf NMI watchdog permanently disabled
[    0.502309] smp: Bringing up secondary CPUs ...
[    0.502759] installing Xen timer for CPU 2
[    0.503384] installing Xen timer for CPU 4
[    0.503838] cpu 2 spinlock event irq 16
[    0.503870] cpu 4 spinlock event irq 17
[    0.504867] installing Xen timer for CPU 1
[    0.505495] installing Xen timer for CPU 3
[    0.506125] installing Xen timer for CPU 5
[    0.506363] cpu 1 spinlock event irq 33
[    0.507869] cpu 3 spinlock event irq 34
[    0.507901] cpu 5 spinlock event irq 35
[    0.507923] smp: Brought up 1 node, 6 CPUs
-- snap --



thank you very much!


niels.


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