linux-kernel - Re: [PATCH] KVM: x86: fix bogus warning about reserved bits

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Message-ID: <5604FC96.1010707@redhat.com>
Date:	Fri, 25 Sep 2015 09:49:42 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Borislav Petkov <bp@...en8.de>,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: fix bogus warning about reserved bits



On 24/09/2015 12:12, Borislav Petkov wrote:
> On Thu, Sep 24, 2015 at 11:23:08AM +0800, Xiao Guangrong wrote:
>>> +static inline bool
>>> +boot_cpu_is_amd(void)
>>> +{
>>> +	WARN_ON_ONCE(!tdp_enabled);
>>> +	return shadow_x_mask != 0;
>>
>> shadow_x_mask != 0 is Intel's CPU.
>>
>> Borislav, could you please check shadow_x_mask == 0 instead and test it again?
> 
> That did the trick:
> 
> [   62.640392] kvm: zapping shadow pages for mmio generation wraparound
> [   63.100301] cpuid(0).ebx = 68747541
> [   63.193426] kvm [3748]: vcpu0 unhandled rdmsr: 0xc0010112
> [   64.538294] kvm [3748]: vcpu0 unhandled rdmsr: 0xc0011021
> [   64.866263] kvm [3748]: vcpu1 unhandled rdmsr: 0xc0011021
> [   64.971972] kvm [3748]: vcpu2 unhandled rdmsr: 0xc0011021
> [   65.070376] kvm [3748]: vcpu3 unhandled rdmsr: 0xc0011021
> [   65.170625] kvm [3748]: vcpu4 unhandled rdmsr: 0xc0011021
> [   65.272838] kvm [3748]: vcpu5 unhandled rdmsr: 0xc0011021
> [   65.374288] kvm [3748]: vcpu6 unhandled rdmsr: 0xc0011021
> [   65.474825] kvm [3748]: vcpu7 unhandled rdmsr: 0xc0011021
> 
> That's all I got in dmesg from booting the guest - no more mmio PF
> warnings.

Great, though this doesn't yet explain why guest_cpuid_is_amd failed.
I'll look into it next week when Amazon delivers my shiny new AMD
mini-PC :) and send the patch to Linus meanwhile.

Paolo
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