linux-kernel - Re: [PATCH RESEND 3/3] KVM: Add flush_on

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Date:   Thu, 9 Nov 2017 20:31:00 +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 RESEND 3/3] KVM: Add flush_on_enter before guest enter

2017-11-09 18:54 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
> On 09/11/2017 03:02, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> PV-Flush guest would indicate to flush on enter, flush the TLB before
>> entering and exiting the guest.
>>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>>  arch/x86/kvm/x86.c | 12 ++++++++++--
>>  1 file changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 1ea28a2..f295360 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -2116,7 +2116,13 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
>>               &vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
>>               return;
>>
>> -     vcpu->arch.st.steal.preempted = KVM_VCPU_NOT_PREEMPTED;
>> +     if (xchg(&vcpu->arch.st.steal.preempted, KVM_VCPU_NOT_PREEMPTED) ==
>> +                     (KVM_VCPU_SHOULD_FLUSH | KVM_VCPU_PREEMPTED))
>> +             /*
>> +              * Do TLB_FLUSH before entering the guest, its passed
>> +              * the stage of request checking
>> +              */
>> +             kvm_x86_ops->tlb_flush(vcpu);
>>
>>       if (vcpu->arch.st.steal.version & 1)
>>               vcpu->arch.st.steal.version += 1;  /* first time write, random junk */
>> @@ -2887,7 +2893,9 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
>>       if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
>>               return;
>>
>> -     vcpu->arch.st.steal.preempted = KVM_VCPU_PREEMPTED;
>> +     if (xchg(&vcpu->arch.st.steal.preempted, KVM_VCPU_PREEMPTED) ==
>> +                             KVM_VCPU_SHOULD_FLUSH)
>> +             kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
>
> This is not necessary.  Instead, you can just OR the KVM_VCPU_PREEMPTED
> bit; record_steal_time will pick up the request and do the TLB flush later.
>
> Also, I think this is a case where you should prefer INVVPID to INVEP.
> That's because "execution of the INVEPT instruction invalidates
> guest-physical mappings and combined mappings" while "execution of the
> INVVPID instruction invalidates linear mappings and combined mappings".
> In this case, invalidating guest-physical mapping is unnecessary.
>
> So you could add a new bool argument to kvm_x86_ops->tlb_flush.  In
> vmx.c, __vmx_flush_tlb can do invept if "enable_ept && (invalidate_gpa
> || !enable_vpid)".

Agreed.

Regards,
Wanpeng Li