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Re: [PATCH] target/i386: relax assert when old host kernels don't includ

From: Paolo Bonzini
Subject: Re: [PATCH] target/i386: relax assert when old host kernels don't include msrs
Date: Wed, 4 Dec 2019 17:23:50 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1

On 04/12/19 16:47, Eduardo Habkost wrote:
> On Wed, Dec 04, 2019 at 04:34:45PM +0100, Paolo Bonzini wrote:
>> On 04/12/19 16:07, Catherine Ho wrote:
>>>> Ok, so the problem is that some MSR didn't exist in that version.  Which
>>> I thought in my platform, the only MSR didn't exist is MSR_IA32_VMX_BASIC
>>> (0x480). If I remove this kvm_msr_entry_add(), everything is ok, the guest 
>>> can
>>> be boot up successfully.
>> MSR_IA32_VMX_BASIC was added in kvm-4.10.  Maybe the issue is the
>> _value_ that is being written to the VM is not valid?  Can you check
>> what's happening in vmx_restore_vmx_basic?
> I believe env->features[FEAT_VMX_BASIC] will be initialized to 0
> if the host kernel doesn't have KVM_CAP_GET_MSR_FEATURES.

But the host must have MSR features if the MSRs are added:

        if (kvm_feature_msrs && cpu_has_vmx(env)) {
            kvm_msr_entry_add_vmx(cpu, env->features);

Looks like feature MSRs were backported to 4.14, but
1389309c811b0c954bf3b591b761d79b1700283d and the previous commit weren't.


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