linux-kernel - Re: [PATCH v3 2/9] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F

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Message-ID: <166936633695.19077.13372353298394327779@t14-nrb.local>
Date:   Fri, 25 Nov 2022 09:52:18 +0100
From:   Nico Boehr <nrb@...ux.ibm.com>
To:     Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Janis Schoetterl-Glausch <scgl@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Thomas Huth <thuth@...hat.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Jonathan Corbet <corbet@....net>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-s390@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH v3 2/9] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F_CMPXCHG

Quoting Janis Schoetterl-Glausch (2022-11-22 14:10:41)
> On Tue, 2022-11-22 at 08:47 +0100, Thomas Huth wrote:
> > On 17/11/2022 23.17, Janis Schoetterl-Glausch wrote:
[...]
> > >   Supported flags:
> > >     * ``KVM_S390_MEMOP_F_CHECK_ONLY``
> > >     * ``KVM_S390_MEMOP_F_SKEY_PROTECTION``
> > > +  * ``KVM_S390_MEMOP_F_CMPXCHG``
> > > +
> > > +The semantics of the flags common with logical acesses are as for logical
> > > +accesses.
> > > +
> > > +For write accesses, the KVM_S390_MEMOP_F_CMPXCHG might be supported.
> > 
> > I'd maybe merge this with the last sentence:
> > 
> > For write accesses, the KVM_S390_MEMOP_F_CMPXCHG flag is supported if 
> > KVM_CAP_S390_MEM_OP_EXTENSION has bit 1 (i.e. bit with value 2) set.
> 
> Ok.
> > 
> > ... and speaking of that, I wonder whether it's maybe a good idea to 
> > introduce some #defines for bit 1 / value 2, to avoid the confusion ?
> 
> Not sure, I don't feel it's too complicated. Where would you define it?
> Next to the mem_op struct? KVM_S390_MEMOP_EXTENSION_CAP_CMPXCHG?

I think the define would be a good idea. Location and name sound good to me.

You could also replace the hard-coded 0x3 in kvm_vm_ioctl_check_extension() when you have the define.