linux-kernel - Re: [PATCH] KVM: nVMX: consult PFER_MASK and PFER

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Date:   Mon, 24 Jul 2017 21:57:45 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH] KVM: nVMX: consult PFER_MASK and PFER_MATCH before nested
 vmexit if inject #PF

2017-07-24 21:36 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
> On 23/07/2017 03:05, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> When generating #PF VM-exit, check equality:
>> (PFEC & PFEC_MASK) == PFEC_MATCH
>> If there is equality, the 14 bit of exception bitmap is used to take decision
>> about generating #PF VM-exit. If there is inequality, inverted 14 bit is used.
>>
>> Reported-by: Jim Mattson <jmattson@...gle.com>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>>  arch/x86/kvm/vmx.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 29fd8af..8a213f2 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -2429,6 +2429,8 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
>>       vmx_set_interrupt_shadow(vcpu, 0);
>>  }
>>
>> +static bool nested_vmx_is_page_fault_vmexit(struct vmcs12 *vmcs12, u16 error_code);
>> +
>>  /*
>>   * KVM wants to inject page-faults which it got to the guest. This function
>>   * checks whether in a nested guest, we need to inject them to L1 or L2.
>> @@ -2442,6 +2444,10 @@ static int nested_vmx_check_exception(struct kvm_vcpu *vcpu)
>>               (nr == PF_VECTOR && vcpu->arch.exception.nested_apf)))
>>               return 0;
>>
>> +     if (nr == PF_VECTOR && !vcpu->arch.exception.nested_apf &&
>> +             !nested_vmx_is_page_fault_vmexit(vmcs12, vcpu->arch.exception.error_code))
>> +             return 0;
>
> This is wrong, the check must replace "(vmcs12->exception_bitmap & (1u
> << nr)" if nr == PF_VECTOR.

How about something like this:

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 29fd8af..52afd23 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2439,7 +2439,8 @@ static int nested_vmx_check_exception(struct
kvm_vcpu *vcpu)
     unsigned int nr = vcpu->arch.exception.nr;

     if (!((vmcs12->exception_bitmap & (1u << nr)) ||
-        (nr == PF_VECTOR && vcpu->arch.exception.nested_apf)))
+        (nr == PF_VECTOR && (vcpu->arch.exception.nested_apf ||
+            nested_vmx_is_page_fault_vmexit(vmcs12,
vcpu->arch.exception.error_code)))))
         return 0;

     if (vcpu->arch.exception.nested_apf) {

Regards,
Wanpeng Li