From: "Jan Beulich" <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Juergen Gross <jgross@suse.com>, Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH v2 for-4.11] x86/spec_ctrl: Updates to retpoline-safety decision making
Date: Thu, 19 Apr 2018 09:02:49 -0600 [thread overview]
Message-ID: <5AD8AF9902000078001BCB5A@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <1524147939-17421-1-git-send-email-andrew.cooper3@citrix.com>
>>> On 19.04.18 at 16:25, <andrew.cooper3@citrix.com> wrote:
> All of this is as recommended by the Intel whitepaper:
>
> https://software.intel.com/sites/default/files/managed/1d/46/Retpoline-A-Branch-Target-Injection-Mitigation.pdf
>
> The 'RSB Alternative' bit in MSR_ARCH_CAPABILITIES may be set by a hypervisor
> to indicate that the virtual machine may migrate to a processor which isn't
> retpoline-safe. Introduce a shortened name (to reduce code volume), treat it
> as authorative in retpoline_safe(), and print its value along with the other
> ARCH_CAPS bits.
>
> The exact processor models which do have RSB semantics which fall back to BTB
> predictions are enumerated, and include Kabylake and Coffeelake. Leave a
> printk() in the default case to help identify cases which aren't covered.
>
> The exact microcode versions from Broadwell RSB-safety are taken from the
> referenced microcode update file (adjusting for the known-bad microcode
> versions). Despite the exact wording of the text, it is only Broadwell
> processors which need a microcode check.
>
> In practice, this means that all Broadwell hardware with up-to-date microcode
> will use retpoline in preference to IBRS, which will be a performance
> improvement for desktop and server systems which would previously always opt
> for IBRS over retpoline.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
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next prev parent reply other threads:[~2018-04-19 15:02 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-18 18:13 [PATCH for-4.11] x86/spec_ctrl: Updates to retpoline-safety decision making Andrew Cooper
2018-04-19 9:00 ` Jan Beulich
2018-04-19 10:26 ` Andrew Cooper
2018-04-19 12:04 ` Jan Beulich
2018-04-19 14:25 ` [PATCH v2 " Andrew Cooper
2018-04-19 15:02 ` Jan Beulich [this message]
2018-04-19 15:15 ` Juergen Gross
2018-04-23 21:16 ` [PATCH " Konrad Rzeszutek Wilk
2018-04-23 23:09 ` Andrew Cooper
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