linux-kernel - Re: [PATCH RFC 2/6] KVM: x86: extend struct kvm_vcpu_pv_apf

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Date:   Tue, 05 May 2020 10:08:09 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Gavin Shan <gshan@...hat.com>, x86@...nel.org, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH RFC 2/6] KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info

Gavin Shan <gshan@...hat.com> writes:

> Hi Vitaly,
>
> On 4/29/20 7:36 PM, Vitaly Kuznetsov wrote:
>> Currently, APF mechanism relies on the #PF abuse where the token is being
>> passed through CR2. If we switch to using interrupts to deliver page-ready
>> notifications we need a different way to pass the data. Extent the existing
>> 'struct kvm_vcpu_pv_apf_data' with token information.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> ---
>>   arch/x86/include/uapi/asm/kvm_para.h |  3 ++-
>>   arch/x86/kvm/x86.c                   | 10 ++++++----
>>   2 files changed, 8 insertions(+), 5 deletions(-)
>> 
>> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
>> index 2a8e0b6b9805..df2ba34037a2 100644
>> --- a/arch/x86/include/uapi/asm/kvm_para.h
>> +++ b/arch/x86/include/uapi/asm/kvm_para.h
>> @@ -113,7 +113,8 @@ struct kvm_mmu_op_release_pt {
>>   
>>   struct kvm_vcpu_pv_apf_data {
>>   	__u32 reason;
>> -	__u8 pad[60];
>> +	__u32 token;
>> +	__u8 pad[56];
>>   	__u32 enabled;
>>   };
>>   
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index b93133ee07ba..7c21c0cf0a33 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -2662,7 +2662,7 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
>>   	}
>>   
>>   	if (kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.apf.data, gpa,
>> -					sizeof(u32)))
>> +					sizeof(u64)))
>>   		return 1;
>>   
>>   	vcpu->arch.apf.send_user_only = !(data & KVM_ASYNC_PF_SEND_ALWAYS);
>> @@ -10352,8 +10352,9 @@ static void kvm_del_async_pf_gfn(struct kvm_vcpu *vcpu, gfn_t gfn)
>>   	}
>>   }
>>   
>> -static int apf_put_user(struct kvm_vcpu *vcpu, u32 val)
>> +static int apf_put_user(struct kvm_vcpu *vcpu, u32 reason, u32 token)
>>   {
>> +	u64 val = (u64)token << 32 | reason;
>>   
>>   	return kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.apf.data, &val,
>>   				      sizeof(val));
>> @@ -10405,7 +10406,8 @@ void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
>>   	kvm_add_async_pf_gfn(vcpu, work->arch.gfn);
>>   
>>   	if (kvm_can_deliver_async_pf(vcpu) &&
>> -	    !apf_put_user(vcpu, KVM_PV_REASON_PAGE_NOT_PRESENT)) {
>> +	    !apf_put_user(vcpu, KVM_PV_REASON_PAGE_NOT_PRESENT,
>> +			  work->arch.token)) {
>>   		fault.vector = PF_VECTOR;
>>   		fault.error_code_valid = true;
>>   		fault.error_code = 0;
>> @@ -10438,7 +10440,7 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
>>   	trace_kvm_async_pf_ready(work->arch.token, work->cr2_or_gpa);
>>   
>>   	if (vcpu->arch.apf.msr_val & KVM_ASYNC_PF_ENABLED &&
>> -	    !apf_put_user(vcpu, KVM_PV_REASON_PAGE_READY)) {
>> +	    !apf_put_user(vcpu, KVM_PV_REASON_PAGE_READY, work->arch.token)) {
>>   			fault.vector = PF_VECTOR;
>>   			fault.error_code_valid = true;
>>   			fault.error_code = 0;
>> 
>
> It would be as below based on two facts: (1) token is more important than reason;
> (2) token will be put into high word of @val. I think apf_{get,put}_user() might
> be worthy to be inline. However, it's not a big deal.

This is to be changed in v1 as we agreed to drop page-ready delivery via
#PF completely.

>     static inline int apf_put_user(struct kvm_vcpu *vcpu, u32 token, u32 reason)
>

Yes, it makes sense to inline these. Thanks!

-- 
Vitaly