From: Peter Zijlstra <peterz@infradead.org>
To: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
xen-devel@lists.xenproject.org,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [Xen-devel] [PATCH] x86/xen: disable nosmt in Xen guests
Date: Wed, 12 Jun 2019 13:48:36 +0200 [thread overview]
Message-ID: <20190612114836.GI3436@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190612101228.23898-1-jgross@suse.com>
On Wed, Jun 12, 2019 at 12:12:28PM +0200, Juergen Gross wrote:
> When running as a Xen guest selecting "nosmt" either via command line
> or implicitly via default settings makes no sense, as the guest has no
> clue about the real system topology it is running on. With Xen it is
> the hypervisor's job to ensure the proper bug mitigations are active
> regarding smt settings.
>
> So when running as a Xen guest set cpu_smt_control to "not supported"
> in order to avoid disabling random vcpus.
If it doesn't make sense; then the topology should not expose SMT
threads and the knob will not have any effect.
If you expose SMT topology info to the guest, then you get what you ask
for.
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next prev parent reply other threads:[~2019-06-12 13:07 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-12 10:12 [Xen-devel] [PATCH] x86/xen: disable nosmt in Xen guests Juergen Gross
2019-06-12 10:19 ` Jan Beulich
2019-06-12 10:36 ` Juergen Gross
2019-06-12 11:48 ` Peter Zijlstra [this message]
2019-06-12 14:59 ` Juergen Gross
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