linux-kernel - Re: [PATCH 1/2] kvm: vmx: Use basic exit reason to check if it's the specific VM EXIT

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Message-ID: <87imjwp24x.fsf@vitty.brq.redhat.com>
Date:   Mon, 24 Feb 2020 14:04:46 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH 1/2] kvm: vmx: Use basic exit reason to check if it's the specific VM EXIT

Xiaoyao Li <xiaoyao.li@...el.com> writes:

> On 2/24/2020 6:16 PM, Vitaly Kuznetsov wrote:
>> Xiaoyao Li <xiaoyao.li@...el.com> writes:
>> 

...

>>>   		rip = kvm_rip_read(vcpu);
>>>   		rip += vmcs_read32(VM_EXIT_INSTRUCTION_LEN);
>>>   		kvm_rip_write(vcpu, rip);
>>> @@ -5797,6 +5797,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
>>>   {
>>>   	struct vcpu_vmx *vmx = to_vmx(vcpu);
>>>   	u32 exit_reason = vmx->exit_reason;
>>> +	u16 basic_exit_reason = basic(exit_reason);
>> 
>> I don't think renaming local variable is needed, let's just do
>> 
>> 'u16 exit_reason = basic_exit_reason(vmx->exit_reason)' and keep the
>> rest of the code as-is.
>
> No, we can't do this.
>
> It's not just renaming local variable, the full 32-bit exit reason is 
> used elsewhere in this function that needs the upper 16-bit.
>
> Here variable basic_exit_reason is added for the cases where only basic 
> exit reason number is needed.
>

Can we do the other way around, i.e. introduce 'extended_exit_reason'
and use it where all 32 bits are needed? I'm fine with the change, just
trying to minimize the (unneeded) code churn.

-- 
Vitaly