Re: [PATCH] kvm: x86: rewrite kvm_spec_ctrl_valid_bits

Paolo Bonzini
2020-07-07T17:26:47Z

On 07/07/20 13:30, Maxim Levitsky wrote:
>> Somehwat crazy idea inbound... rather than calculating the valid bits in
>> software, what if we throw the value at the CPU and see if it fails? At
>> least that way the host and guest are subject to the same rules. E.g.
>>
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -2062,11 +2062,19 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>> !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
>> return 1;
>>
>> - if (data & ~kvm_spec_ctrl_valid_bits(vcpu))
>> - return 1;
>> -
>> + ret = 0;
>> vmx->spec_ctrl = data;
>> - if (!data)
>> +
>> + local_irq_disable();
>> + if (rdmsrl_safe(MSR_IA32_SPEC_CTRL, &data))
>> + ret = 1;
>> + else if (wrmsrl_safe(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl))
>> + ret = 1;
>> + else
>> + wrmsrl(MSR_IA32_SPEC_CTRL, data))
>> + local_irq_enable();
>> +
>> + if (ret || !vmx->spec_ctrl)
>> break;
>>
>> /*
>>
> I don't mind this as well, knowing that this is done only one per VM run anyway.

Maxim, this is okay as well; can you send a patch for it?

Paolo