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

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Date:   Tue, 6 Sep 2016 08:45:11 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Jan Dakinevich <jan.dakinevich@...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

2016-09-05 21:02 GMT+08:00 Jan Dakinevich <jan.dakinevich@...il.com>:
>
>
> 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.

Agreed, I misread guest_linear_address as guest_physical_address.

>
>> 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.

Thanks for the patch.

Reviewed-by: Wanpeng Li <wanpeng.li@...mail.com>