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

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 02/07/2011 04:15, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

>> 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.

Oops, I forgot to remove the redundant second BUG_ON. I'll do that now.
Thanks!

 -- Keir

> Thanks
> Kevin



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