linux-kernel - Re: [PATCH] KVM: nVMX: pass valid guest linear-address to the L1

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Date:   Mon, 5 Sep 2016 16:02:41 +0300
From:   Jan Dakinevich <jan.dakinevich@...il.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        ynorov@...iumnetworks.com
Subject: Re: [PATCH] KVM: nVMX: pass valid guest linear-address to the L1



On 09/05/2016 03:49 AM, Wanpeng Li wrote:
> 2016-09-05 2:22 GMT+08:00 Jan Dakinevich <jan.dakinevich@...il.com>:
>> If EPT support is exposed to L1 hypervisor, guest linear-address field
>> of VMCS should contain GVA of L2, the access to which caused EPT violation.
>>
>> Signed-off-by: Jan Dakinevich <jan.dakinevich@...il.com>
>> ---
>>  arch/x86/kvm/vmx.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 5cede40..a4bb2bd 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -10500,6 +10500,9 @@ static void prepare_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
>>                 vmcs12->guest_pdptr3 = vmcs_read64(GUEST_PDPTR3);
>>         }
>>
>> +       if (nested_cpu_has_ept(vmcs12))
>> +               vmcs12->guest_linear_address = vmcs_readl(GUEST_LINEAR_ADDRESS);
>> +
> 
> No, nested_ept_inject_page_fault() will set
> vmcs12->guest_linear_address after L0 walks L1's EPT page table and
> finds that the mapping is invalid if nested EPT is enabled.

Acctually, nested_ept_inject_page_fault() doesn't do that, the routine
sets only vmcs12->guest_physical_address, but
vmcs12->guest_linear_address remains untouched. As result, after EPT
fault from L2, vmcs_readl(GUEST_LINEAR_ADDRESS) in L1 always returns 0.

> prepare_vmcs12() just copies the vmcs field that could have changed by
> the L2 guest or the exit-information etc instead of all fields since
> other fields are modified by L1 with VMWRITE, which already writes to
> vmcs12 directly.

Yes, and guest linear-address considered as a part of exit information,
provided by hardware.

> 
> Regards,
> Wanpeng Li
> 

-- 
Best regards
Jan Dakinevich