linux-kernel - Re: [RFC PATCH v5 083/104] KVM: x86: Split core of hypercall emulation to helper function

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Message-ID: <1eac9040-f75f-8838-bd75-521cb666c61a@redhat.com>
Date:   Thu, 7 Apr 2022 15:12:57 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sagi Shahar <sagis@...gle.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        isaku.yamahata@...il.com, Jim Mattson <jmattson@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 083/104] KVM: x86: Split core of hypercall
 emulation to helper function

On 3/21/22 19:32, Sagi Shahar wrote:
> On Fri, Mar 4, 2022 at 12:00 PM <isaku.yamahata@...el.com> wrote:
>>
>> From: Sean Christopherson <sean.j.christopherson@...el.com>
>>
>> By necessity, TDX will use a different register ABI for hypercalls.
>> Break out the core functionality so that it may be reused for TDX.
>>
>> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
>> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
>> ---
>>   arch/x86/include/asm/kvm_host.h |  4 +++
>>   arch/x86/kvm/x86.c              | 54 ++++++++++++++++++++-------------
>>   2 files changed, 37 insertions(+), 21 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 8dab9f16f559..33b75b0e3de1 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -1818,6 +1818,10 @@ void kvm_request_apicv_update(struct kvm *kvm, bool activate,
>>   void __kvm_request_apicv_update(struct kvm *kvm, bool activate,
>>                                  unsigned long bit);
>>
>> +unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr,
>> +                                     unsigned long a0, unsigned long a1,
>> +                                     unsigned long a2, unsigned long a3,
>> +                                     int op_64_bit);
>>   int kvm_emulate_hypercall(struct kvm_vcpu *vcpu);
>>
>>   int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 314ae43e07bf..9acb33a17445 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -9090,26 +9090,15 @@ static int complete_hypercall_exit(struct kvm_vcpu *vcpu)
>>          return kvm_skip_emulated_instruction(vcpu);
>>   }
>>
>> -int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>> +unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr,
>> +                                     unsigned long a0, unsigned long a1,
>> +                                     unsigned long a2, unsigned long a3,
>> +                                     int op_64_bit)
>>   {
>> -       unsigned long nr, a0, a1, a2, a3, ret;
>> -       int op_64_bit;
>> -
>> -       if (kvm_xen_hypercall_enabled(vcpu->kvm))
>> -               return kvm_xen_hypercall(vcpu);
>> -
>> -       if (kvm_hv_hypercall_enabled(vcpu))
>> -               return kvm_hv_hypercall(vcpu);

Please keep Xen and Hyper-V hypercalls to kvm_emulate_hypercall (more on 
this in the reply to patch 89).  __kvm_emulate_hypercall should only 
handle KVM hypercalls.

>> +       if (static_call(kvm_x86_get_cpl)(vcpu) != 0) {
>> +               ret = -KVM_EPERM;
>> +               goto out;
>> +       }

Is this guaranteed by TDG.VP.VMCALL?

Paolo

>> +       ret = __kvm_emulate_hypercall(vcpu, nr, a0, a1, a2, a3, op_64_bit);
>>   out:
>>          if (!op_64_bit)
>>                  ret = (u32)ret;
>> --
>> 2.25.1
>>
> 
> Sagi
>