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Message-ID: <e6b80db6-bfc8-47c7-94f0-673884646b80@linux.intel.com>
Date: Thu, 9 May 2024 11:26:13 +0800
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Subject: Re: [PATCH v19 097/130] KVM: x86: Split core of hypercall emulation
 to helper function
To: Isaku Yamahata <isaku.yamahata@intel.com>, Chao Gao <chao.gao@intel.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
 isaku.yamahata@gmail.com, Paolo Bonzini <pbonzini@redhat.com>,
 erdemaktas@google.com, Sean Christopherson <seanjc@google.com>,
 Sagi Shahar <sagis@google.com>, Kai Huang <kai.huang@intel.com>,
 chen.bo@intel.com, hang.yuan@intel.com, tina.zhang@intel.com,
 Sean Christopherson <sean.j.christopherson@intel.com>,
 isaku.yamahata@linux.intel.com
References: <cover.1708933498.git.isaku.yamahata@intel.com>
 <d6547bd0c1eccdfb4a4908e330cc56ad39535f5e.1708933498.git.isaku.yamahata@intel.com>
 <ZgY0hy6Io72yZ9dF@chao-email>
 <20240403183420.GI2444378@ls.amr.corp.intel.com>
From: Binbin Wu <binbin.wu@linux.intel.com>
In-Reply-To: <20240403183420.GI2444378@ls.amr.corp.intel.com>
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On 4/4/2024 2:34 AM, Isaku Yamahata wrote:
> On Fri, Mar 29, 2024 at 11:24:55AM +0800,
> Chao Gao <chao.gao@intel.com> wrote:
>
>> On Mon, Feb 26, 2024 at 12:26:39AM -0800, isaku.yamahata@intel.com wrote:
>>> +
>>> +int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>>> +{
>>> +	unsigned long nr, a0, a1, a2, a3, ret;
>>> +	int op_64_bit;
>>> +	int cpl;
>>> +
>>> +	if (kvm_xen_hypercall_enabled(vcpu->kvm))
>>> +		return kvm_xen_hypercall(vcpu);
>>> +
>>> +	if (kvm_hv_hypercall_enabled(vcpu))
>>> +		return kvm_hv_hypercall(vcpu);
>>> +
>>> +	nr = kvm_rax_read(vcpu);
>>> +	a0 = kvm_rbx_read(vcpu);
>>> +	a1 = kvm_rcx_read(vcpu);
>>> +	a2 = kvm_rdx_read(vcpu);
>>> +	a3 = kvm_rsi_read(vcpu);
>>> +	op_64_bit = is_64_bit_hypercall(vcpu);
>>> +	cpl = static_call(kvm_x86_get_cpl)(vcpu);
>>> +
>>> +	ret = __kvm_emulate_hypercall(vcpu, nr, a0, a1, a2, a3, op_64_bit, cpl);
>>> +	if (nr == KVM_HC_MAP_GPA_RANGE && !ret)
>>> +		/* MAP_GPA tosses the request to the user space. */
>> no need to check what the request is. Just checking the return value will suffice.
> This is needed to avoid updating rax etc.  KVM_HC_MAP_GPA_RANGE is only an
> exception to go to the user space.  This check is a bit weird, but I couldn't
> find a good way.

To be generic, I think we can use
"vcpu->kvm->arch.hypercall_exit_enabled & (1 << nr)" to check if it 
needs to exit to userspace.

i.e.,

+       ...
+       ret = __kvm_emulate_hypercall(vcpu, nr, a0, a1, a2, a3, 
op_64_bit, cpl);
+       if (!ret && (vcpu->kvm->arch.hypercall_exit_enabled & (1 << nr)))
+               /* The hypercall is requested to exit to userspace. */
+               return 0;

>
>>> +		return 0;
>>> +
>>> 	if (!op_64_bit)
>>> 		ret = (u32)ret;
>>> 	kvm_rax_write(vcpu, ret);
>>>
>>> -	++vcpu->stat.hypercalls;
>>> 	return kvm_skip_emulated_instruction(vcpu);
>>> }
>>> EXPORT_SYMBOL_GPL(kvm_emulate_hypercall);
>>> -- 
>>> 2.25.1
>>>
>>>