From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Juergen Gross <jgross@suse.com>,
Ian Jackson <Ian.Jackson@eu.citrix.com>,
Wei Liu <wei.liu2@citrix.com>,
xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH] libxc/x86: don't hand through CPUID leaf 0x80000008 as is
Date: Thu, 17 May 2018 14:47:56 +0100 [thread overview]
Message-ID: <134f1870-31f6-35ba-4d69-2e18ab8003f6@citrix.com> (raw)
In-Reply-To: <5AFD85CA02000078001C3A3B@prv1-mh.provo.novell.com>
On 17/05/18 14:38, Jan Beulich wrote:
>>>> On 17.05.18 at 15:26, <andrew.cooper3@citrix.com> wrote:
>> On 17/05/18 14:20, Jan Beulich wrote:
>>> Just like for HVM the feature set should be used for EBX output, while
>>> EAX should be restricted to the low 16 bits and ECX/EDX should be zero.
>>>
>>> Short of there being white listing in place just like on the HVM side,
>>> also zap leaves 6, 9, and 0x80000007 as well as unknown / reserved ones.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> Do you want this for backporting?
> Not really, at least that wasn't a primary goal.
>
>> The changes below are enforced by recalculate_cpuid_policy() (and in
>> particular, recaluclate_misc()) in the hypervisor for the past few
>> releases, and Sergey is currently in the process of making all of this
>> libxc logic disappear.
> Well, maybe I'm simply confused: Commit d297b56682 ("x86/cpuid: Handling
> of IBRS/IBPB, STIBP and IBRS for guests") introduced similar code into
> xc_cpuid_hvm_policy() without doing the same for xc_cpuid_pv_policy().
> That's pretty recent a commit, and one that has been backported all the
> way through to 4.6. Are you saying that was a pointless change then?
No sorry - you're completely correct.
Without the PV side, a guest will by default get the same settings as
dom0. The reason why my XTF tests doesn't notice this is because libxl
uses a separate path, and XenServer uses a yet-different path.
The PV side wants to gain a matching clzero hunk.
My comment about recalculate_cpuid_policy() applies to the clamping part
of the change.
~Andrew
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prev parent reply other threads:[~2018-05-17 13:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-17 13:20 [PATCH] libxc/x86: don't hand through CPUID leaf 0x80000008 as is Jan Beulich
2018-05-17 13:26 ` Andrew Cooper
2018-05-17 13:38 ` Jan Beulich
2018-05-17 13:47 ` Andrew Cooper [this message]
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