linux-kernel - Re: [PATCH 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor

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Message-ID: <jpg4ltowhna.fsf@linux.bootlegged.copy>
Date:   Thu, 03 Aug 2017 15:55:21 -0400
From:   Bandan Das <bsd@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
        rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor

Paolo Bonzini <pbonzini@...hat.com> writes:

> On 03/08/2017 13:39, David Hildenbrand wrote:
>>> +	/* AD, if set, should be supported */
>>> +	if ((address & VMX_EPT_AD_ENABLE_BIT)) {
>>> +		if (!enable_ept_ad_bits)
>>> +			return false;
>> In theory (I guess) we would have to check here if
>> (vmx->nested.nested_vmx_ept_caps & VMX_EPT_AD_BIT)
>
> Yes, that's a more correct check than enable_ept_ad_bits.
>
>>>
>>> +	page = nested_get_page(vcpu, vmcs12->eptp_list_address);
>>> +	if (!page)
>>> +		return 1;
>>> +
>>> +	l1_eptp_list = kmap(page);
>>> +	address = l1_eptp_list[index];
>>> +	accessed_dirty = !!(address & VMX_EPT_AD_ENABLE_BIT);
>> 
>> Minor nit: Can't you directly do
>> 
>> kunmap(page);
>> nested_release_page_clean(page);
>> 
>> at this point?
>> 
>> We can fix this up later.
>
> You actually can do simply kvm_vcpu_read_guest_page(vcpu,
> vmcs12->eptp_list_address >> PAGE_SHIFT, &address, index * 8, 8).

Thanks Paolo, for the interesting tip. David, I sent a new version with the correct
check for AD and using this instead of kmap(page).

> Paolo