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

Binbin Wu
2024-05-09T03:26:20Z

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
>>>
>>>