linux-kernel - Re: [PATCH v1 3/9] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F

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Date:   Wed, 5 Oct 2022 08:27:26 +0200
From:   Thomas Huth <thuth@...hat.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...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 v1 3/9] Documentation: KVM: s390: Describe
 KVM_S390_MEMOP_F_CMPXCHG

On 04/10/2022 20.51, Janis Schoetterl-Glausch wrote:
> On Tue, 2022-10-04 at 10:16 +0200, Thomas Huth wrote:
>> On 30/09/2022 23.07, Janis Schoetterl-Glausch wrote:
>>> Describe the semantics of the new KVM_S390_MEMOP_F_CMPXCHG flag for
>>> absolute vm write memops which allows user space to perform (storage key
>>> checked) cmpxchg operations on guest memory.
>>>
>>> Signed-off-by: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
>>> ---
>>>    Documentation/virt/kvm/api.rst | 18 +++++++++++++++++-
>>>    1 file changed, 17 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
>>> index abd7c32126ce..0e02d66e38ae 100644
>>> --- a/Documentation/virt/kvm/api.rst
>>> +++ b/Documentation/virt/kvm/api.rst
>>> @@ -3771,6 +3771,7 @@ Parameters are specified via the following structure::
>>>    		struct {
> 
> What is the reason you initially didn't copy the /* in */ comment here?

You mean in commit 41408c28f283b ? Uh, don't ask me, that's more than 7 
years ago...

Anyway, please be aware that the MEMOP ioctl is defined as IOW only:

#define KVM_S390_MEM_OP _IOW(KVMIO, 0xb1, struct kvm_s390_mem_op)

... so if you now introduce an "out" field in that struct, this might have 
some impact, e.g. on Valgrind etc.

  Thomas