linux-kernel - Re: [PATCH V2 3/5] KVM/VMX: Add identical ept table pointer check

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Message-ID: <2b0476a7-cb4e-2ced-bbfa-5a72fe523880@microsoft.com>
Date:   Wed, 18 Jul 2018 13:38:38 +0000
From:   Tianyu Lan <Tianyu.Lan@...rosoft.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>
Subject: Re: [PATCH V2 3/5] KVM/VMX: Add identical ept table pointer check

On 7/18/2018 7:59 PM, Paolo Bonzini wrote:
> On 09/07/2018 11:02, Tianyu Lan wrote:
>> +static void check_ept_pointer(struct kvm_vcpu *vcpu, u64 eptp)
>> +{
>> +	struct kvm *kvm = vcpu->kvm;
>> +	u64 tmp_eptp = INVALID_PAGE;
>> +	int i;
>> +
>> +	if (!kvm_x86_ops->tlb_remote_flush)
>> +		return;
>> +
>> +	spin_lock(&to_kvm_vmx(kvm)->ept_pointer_lock);
>> +	to_vmx(vcpu)->ept_pointer = eptp;
>> +
>> +	kvm_for_each_vcpu(i, vcpu, kvm) {
>> +		if (!VALID_PAGE(tmp_eptp)) {
>> +			tmp_eptp = to_vmx(vcpu)->ept_pointer;
>> +		} else if (tmp_eptp != to_vmx(vcpu)->ept_pointer) {
>> +			to_kvm_vmx(kvm)->ept_pointers_match = false;
>> +			spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
>> +			return;
>> +		}
>> +	}
>> +
>> +	to_kvm_vmx(kvm)->ept_pointers_match = true;
>> +	spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
>> +}
>> +
> 
> Is there any reason to do the check here, rather than the first time the
> TLB flush is invoked?  You could:
> 
> - have a tristate (true, false, check) value for ept_pointers_match
> 
> - reset it to "check" in vmx_set_cr3
> 
> - set it to either true or false in tlb_remote_flush if it is check, and
> do the hypercall if it is true.
> 

Thanks for your suggestion. Will update.

> Paolo
>