From: Wei Liu <wei.liu2@citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>, Jan Beulich <JBeulich@suse.com>,
Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH] x86/cpuid: Avoid unconditionally clobbering ITSC for guests
Date: Tue, 17 May 2016 14:12:18 +0100 [thread overview]
Message-ID: <20160517131218.GO8974@citrix.com> (raw)
In-Reply-To: <1463417955-4258-1-git-send-email-andrew.cooper3@citrix.com>
On Mon, May 16, 2016 at 05:59:15PM +0100, Andrew Cooper wrote:
> In general, Invariant TSC is not a feature which can be advertised to guests,
> because it cannot be guaranteed across migrate. domain_cpuid() goes so far as
> to deliberately clobber the feature flag under a number of circumstances.
>
> Because ITSC is absent from the static {pv,hvm}_featureset masks, c/s b648feff
> "xen/x86: Improvements to in-hypervisor cpuid sanity checks" caused ITSC to be
> unconditionally masked out.
>
> As an interim solution, include the hosts idea of ITSC along with the static
> {pv,hvm}_featureset when restricting the guests view of features. This causes
> the hardware domain, and VMs explicitly configured with ITSC and no-migrate to
> be offered ITSC (subject to hardware availability).
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>
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prev parent reply other threads:[~2016-05-17 13:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-16 16:59 [PATCH] x86/cpuid: Avoid unconditionally clobbering ITSC for guests Andrew Cooper
2016-05-17 8:39 ` Jan Beulich
2016-05-17 13:12 ` Wei Liu [this message]
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