Re: [PATCH v1 3/9] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F_CMPXCHG

[Thomas Huth <thuth@redhat.com>]

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@linux.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