Re: [PATCH v1 7/9] memory: introduce RAM_NORESERVE and wire it up in qemu_ram_mmap()

[David Hildenbrand <david@redhat.com>]

On 03.03.21 13:12, Thomas Huth wrote:
> On 03/03/2021 12.37, David Hildenbrand wrote:
>> On 03.03.21 12:35, Cornelia Huck wrote:
>>> On Tue, 2 Mar 2021 20:02:34 +0100
>>> David Hildenbrand <david@redhat.com> wrote:
>>>
>>>> On 02.03.21 18:32, Peter Xu wrote:
>>>>> On Tue, Feb 09, 2021 at 02:49:37PM +0100, David Hildenbrand wrote:
>>>>>> @@ -899,13 +899,17 @@ int kvm_s390_mem_op_pv(S390CPU *cpu, uint64_t
>>>>>> offset, void *hostbuf,
>>>>>>      * to grow. We also have to use MAP parameters that avoid
>>>>>>      * read-only mapping of guest pages.
>>>>>>      */
>>>>>> -static void *legacy_s390_alloc(size_t size, uint64_t *align, bool shared)
>>>>>> +static void *legacy_s390_alloc(size_t size, uint64_t *align, bool shared,
>>>>>> +                               bool noreserve)
>>>>>>     {
>>>>>>         static void *mem;
>>>>>>         if (mem) {
>>>>>>             /* we only support one allocation, which is enough for
>>>>>> initial ram */
>>>>>>             return NULL;
>>>>>> +    } else if (noreserve) {
>>>>>> +        error_report("Skipping reservation of swap space is not
>>>>>> supported.");
>>>>>> +        return NULL
>>>>>
>>>>> Semicolon missing.
>>>>
>>>> Thanks for catching that!
>>>
>>> Regardless of that (and this patch set), can we finally get rid of
>>> legacy_s390_alloc? We already fence off running with a kernel prior to
>>> 3.15, and KVM_CAP_S390_COW depends on ESOP -- are non-ESOP kvm hosts
>>> still relevant? This seems to be a generation 10 feature; do we
>>> realistically expect anyone running this on e.g. a z/VM host that
>>> doesn't provide ESOP?
>>
>> Good question - last time I asked that question (~2 years ago) I was told
>> that such z/VM environemnts are still relevant.
> 
> Now that you've mentioned it ... I've even wrote a blog post about z/VM and
> ESOP some years ago:
> 
>   
> http://people.redhat.com/~thuth/blog/qemu/2017/04/05/s390x-selinux-problem.html
> 
> So if I've got that right again, the z/VM ESOP problem only exists on
> versions older than 6.3. And according to
> https://www.ibm.com/support/lifecycle/search?q=z%2FVM those old versions are
> now unsupported since June 2017 ... thus I guess it's valid to assume that
> nobody is running such an old z/VM version anymore (at least not to use it
> as an environment to run nested KVM guests).

Thanks for that info, I'll send a patch proposing to rip it out - that 
will make things nicer.

-- 
Thanks,

David / dhildenb