linux-kernel - Re: [PATCH v2 3/3] KVM: s390: Increase size of union sca

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Message-ID: <20241126132152.3dc746e7@p-imbrenda>
Date: Tue, 26 Nov 2024 13:21:52 +0100
From: Claudio Imbrenda <imbrenda@...ux.ibm.com>
To: Janosch Frank <frankja@...ux.ibm.com>
Cc: Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger
 <borntraeger@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] KVM: s390: Increase size of union sca_utility to
 four bytes

On Tue, 26 Nov 2024 13:09:56 +0100
Janosch Frank <frankja@...ux.ibm.com> wrote:

> On 11/26/24 11:25 AM, Heiko Carstens wrote:
> [...]
> >   union sca_utility {  
> 
> Would you mind adding a comment?
> 
> 
> ""Utility is defined as 2 bytes but having it 4 bytes wide generates 
> more efficient code. Since the following bytes are reserved this makes 
> no functional difference.""

looks good, thanks!

> 
> > -	__u16 val;
> > +	__u32 val;
> >   	struct {
> > -		__u16 mtcr : 1;
> > -		__u16 reserved : 15;
> > +		__u32 mtcr : 1;
> > +		__u32	   : 31;
> >   	};
> >   };
> >   
> > @@ -107,7 +107,7 @@ struct bsca_block {
> >   	__u64	reserved[5];
> >   	__u64	mcn;
> >   	union sca_utility utility;
> > -	__u8	reserved2[6];
> > +	__u8	reserved2[4];
> >   	struct bsca_entry cpu[KVM_S390_BSCA_CPU_SLOTS];
> >   };
> >   
> > @@ -115,7 +115,7 @@ struct esca_block {
> >   	union ipte_control ipte_control;
> >   	__u64   reserved1[6];
> >   	union sca_utility utility;
> > -	__u8	reserved2[6];
> > +	__u8	reserved2[4];
> >   	__u64   mcn[4];
> >   	__u64   reserved3[20];
> >   	struct esca_entry cpu[KVM_S390_ESCA_CPU_SLOTS];  
>