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[Xen-devel] RE: [PATCH] X86: cpuid faulting feature enable

To: Keir Fraser <keir@xxxxxxx>, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] RE: [PATCH] X86: cpuid faulting feature enable
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Sat, 2 Jul 2011 11:15:25 +0800
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Cc: "Shan, Haitao" <haitao.shan@xxxxxxxxx>, "Li, Xin" <xin.li@xxxxxxxxx>
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Thread-topic: [PATCH] X86: cpuid faulting feature enable
> From: Keir Fraser [mailto:keir.xen@xxxxxxxxx] On Behalf Of Keir Fraser
> Sent: Saturday, July 02, 2011 5:31 AM
> On 01/07/2011 15:32, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
> > X86: cpuid faulting feature enable
> >
> > Latest Intel processor add cpuid faulting feature. This patch is used to
> > support cpuid faulting in Xen.
> > Like cpuid spoofing, cpuid faulting mainly used to support live migration.
> > When cpl>0, cpuid instruction will produce GP, vmm then emulate execution
> of
> > the cpuid instruction. Hence will appear to guest software the value chosen
> by
> > the vmm.
> I fixed this up quite a bit and applied as c/s 23653. Please take a look and
> give it a test. In particular note the changes I made in intel_init(), to
> make sure that APs are at least as featureful as the BSP w.r.t. cpuid
> faulting.

        2.42    +       } else if (boot_cpu_has(X86_FEATURE_CPUID_FAULTING)) {
    2.43 +              BUG_ON(!probe_intel_cpuid_faulting());
    2.44 +              set_bit(X86_FEATURE_CPUID_FAULTING, c->x86_capability);
    2.45 +      }
    2.46 +
    2.47 +      if (!cpu_has_cpuid_faulting)
    2.48 +              set_cpuidmask(c);
    2.49 +
    2.50 +      BUG_ON(cpu_has(c, X86_FEATURE_CPUID_FAULTING) !=
    2.51 +             boot_cpu_has(X86_FEATURE_CPUID_FAULTING));

the latter BUG_ON is useless since if AP is inconsistent with BSP we already
get bug triggered in earlier BUG_ON.


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