From: David Woodhouse <dwmw2@infradead.org>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
KarimAllah Ahmed <karahmed@amazon.de>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Asit Mallick <asit.k.mallick@intel.com>,
Arjan Van De Ven <arjan.van.de.ven@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Andi Kleen <ak@linux.intel.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Dan Williams <dan.j.williams@intel.com>,
Jun Nakajima <jun.nakajima@intel.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Greg KH <gregkh@linuxfoundation.org>,
Andy Lutomirski <luto@kernel.org>,
Ashok Raj <ashok.raj@intel.com>,
daniel.kiper@oracle.com
Subject: Re: [PATCH] x86: vmx: Allow direct access to MSR_IA32_SPEC_CTRL
Date: Sun, 28 Jan 2018 20:39:28 +0000 [thread overview]
Message-ID: <1517171968.6624.80.camel@infradead.org> (raw)
In-Reply-To: <4DCAF18F-C86A-4CBC-A9CC-CC01BF63313F@oracle.com>
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On Sun, 2018-01-28 at 15:21 -0500, Konrad Rzeszutek Wilk wrote:
> >To avoid the overhead of atomically saving and restoring the MSR_IA32_SPEC_CTRL
> >for guests that do not actually use the MSR, only add_atomic_switch_msr when a
> >non-zero is written to it.
>
>
> We tried this and found that it was about 3% slower that doing the
> old way of rdmsr and wrmsr.
>
> But that was also with the host doing IBRS as well.
The common case will be that neither host nor guest are doing IBRS.
Until the guest touches the MSR we do absolutely *nothing* with it,
which is definitely the fastest option.
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next prev parent reply other threads:[~2018-01-28 20:39 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-28 19:29 [PATCH] x86: vmx: Allow direct access to MSR_IA32_SPEC_CTRL KarimAllah Ahmed
2018-01-28 20:21 ` Konrad Rzeszutek Wilk
2018-01-28 20:39 ` David Woodhouse [this message]
2018-01-28 20:40 ` Andy Lutomirski
2018-01-28 20:44 ` David Woodhouse
2018-01-28 20:53 ` Andy Lutomirski
2018-01-28 20:56 ` David Woodhouse
2018-01-28 21:41 ` Van De Ven, Arjan
2018-01-28 21:47 ` David Woodhouse
2018-01-29 1:06 ` KarimAllah Ahmed
2018-01-29 18:43 ` Jim Mattson
2018-01-29 19:01 ` David Woodhouse
2018-01-29 19:04 ` Jim Mattson
2018-01-29 19:10 ` KarimAllah Ahmed
2018-01-29 19:16 ` Konrad Rzeszutek Wilk
2018-01-29 19:27 ` Jim Mattson
-- strict thread matches above, loose matches on Subject: below --
2018-01-29 0:39 Liran Alon
2018-01-29 8:46 ` David Woodhouse
2018-01-29 9:43 ` KarimAllah Ahmed
2018-01-29 10:37 ` David Woodhouse
2018-01-29 10:55 ` Paolo Bonzini
2018-01-29 17:27 ` Konrad Rzeszutek Wilk
2018-01-29 10:47 ` Paolo Bonzini
2018-01-29 17:31 ` Konrad Rzeszutek Wilk
2018-01-29 21:49 ` Daniel Kiper
2018-01-29 23:01 ` Jim Mattson
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