linux-kernel - Re: [PATCH v19 097/130] KVM: x86: Split core of hypercall emulation to helper function

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Message-ID: <e6b80db6-bfc8-47c7-94f0-673884646b80@linux.intel.com>
Date: Thu, 9 May 2024 11:26:13 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Isaku Yamahata <isaku.yamahata@...el.com>, Chao Gao <chao.gao@...el.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
 Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
 chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
 Sean Christopherson <sean.j.christopherson@...el.com>,
 isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 097/130] KVM: x86: Split core of hypercall emulation
 to helper function



On 4/4/2024 2:34 AM, Isaku Yamahata wrote:
> On Fri, Mar 29, 2024 at 11:24:55AM +0800,
> Chao Gao <chao.gao@...el.com> wrote:
>
>> On Mon, Feb 26, 2024 at 12:26:39AM -0800, isaku.yamahata@...el.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
>>>
>>>