linux-kernel - Re: [PATCH 10/10] KVM: VMX: Convert vcpu_vmx.exit

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Message-ID: <4b38ad68-b6fe-0087-25f6-7820588de94d@redhat.com>
Date:   Tue, 17 Mar 2020 18:51:06 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH 10/10] KVM: VMX: Convert vcpu_vmx.exit_reason to a union

On 17/03/20 06:28, Sean Christopherson wrote:
>>>  
>>> +union vmx_exit_reason {
>>> +	struct {
>>> +		u32	basic			: 16;
>>> +		u32	reserved16		: 1;
>>> +		u32	reserved17		: 1;
>>> +		u32	reserved18		: 1;
>>> +		u32	reserved19		: 1;
>>> +		u32	reserved20		: 1;
>>> +		u32	reserved21		: 1;
>>> +		u32	reserved22		: 1;
>>> +		u32	reserved23		: 1;
>>> +		u32	reserved24		: 1;
>>> +		u32	reserved25		: 1;
>>> +		u32	reserved26		: 1;
>>> +		u32	enclave_mode		: 1;
>>> +		u32	smi_pending_mtf		: 1;
>>> +		u32	smi_from_vmx_root	: 1;
>>> +		u32	reserved30		: 1;
>>> +		u32	failed_vmentry		: 1;
>> Just wondering, is there any particular benefit in using 'u32' instead
>> of 'u16' here?
> Not that I know of.  Paranoia that the compiler will do something weird?

Since we have an "u32 full" it makes sense to have u32 here too, it
documents that we're matching an u32 field in the other side of the union.

Paolo