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

[David Hildenbrand]

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