linux-kernel - Re: [PATCH v3 14/37] KVM: x86: Move "flush guest's TLB" logic to separate kvm_x86

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Message-ID: <87ftdw5se4.fsf@vitty.brq.redhat.com>
Date:   Wed, 25 Mar 2020 17:08:35 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ben Gardon <bgardon@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Liran Alon <liran.alon@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        John Haxby <john.haxby@...cle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH v3 14/37] KVM: x86: Move "flush guest's TLB" logic to separate kvm_x86_ops hook

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

> On 25/03/20 11:23, Vitaly Kuznetsov wrote:
>> What do you think about the following (very lightly
>> tested)?
>> 
>> commit 485b4a579605597b9897b3d9ec118e0f7f1138ad
>> Author: Vitaly Kuznetsov <vkuznets@...hat.com>
>> Date:   Wed Mar 25 11:14:25 2020 +0100
>> 
>>     KVM: x86: make Hyper-V PV TLB flush use tlb_flush_guest()
>>     
>>     Hyper-V PV TLB flush mechanism does TLB flush on behalf of the guest
>>     so doing tlb_flush_all() is an overkill, switch to using tlb_flush_guest()
>>     (just like KVM PV TLB flush mechanism) instead. Introduce
>>     KVM_REQ_HV_TLB_FLUSH to support the change.
>>     
>>     Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> 
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 167729624149..8c5659ed211b 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -84,6 +84,7 @@
>>  #define KVM_REQ_APICV_UPDATE \
>>  	KVM_ARCH_REQ_FLAGS(25, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
>>  #define KVM_REQ_TLB_FLUSH_CURRENT	KVM_ARCH_REQ(26)
>> +#define KVM_REQ_HV_TLB_FLUSH		KVM_ARCH_REQ(27)
>>  
>>  #define CR0_RESERVED_BITS                                               \
>>  	(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
>> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
>> index a86fda7a1d03..0d051ed11f38 100644
>> --- a/arch/x86/kvm/hyperv.c
>> +++ b/arch/x86/kvm/hyperv.c
>> @@ -1425,8 +1425,7 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *current_vcpu, u64 ingpa,
>>  	 * vcpu->arch.cr3 may not be up-to-date for running vCPUs so we can't
>>  	 * analyze it here, flush TLB regardless of the specified address space.
>>  	 */
>> -	kvm_make_vcpus_request_mask(kvm,
>> -				    KVM_REQ_TLB_FLUSH | KVM_REQUEST_NO_WAKEUP,
>> +	kvm_make_vcpus_request_mask(kvm, KVM_REQ_HV_TLB_FLUSH,
>>  				    vcpu_mask, &hv_vcpu->tlb_flush);
>>  
>
> Looks good, but why are you dropping KVM_REQUEST_NO_WAKEUP?

My bad, KVM_REQUEST_NO_WAKEUP needs to stay.

-- 
Vitaly