Re: [PATCH v5 6/6] hw/arm/virt: Add 'compact-highmem' property

[Gavin Shan]

Hi Marc,

On 10/20/22 5:44 PM, Marc Zyngier wrote:
> On Thu, 20 Oct 2022 00:57:32 +0100,
> Gavin Shan <gshan@redhat.com> wrote:
> > For Marc's suggestion to add properties so that these high memory
> > regions can be disabled by users. I can add one patch after this one
> > to introduce the following 3 properties. Could you please confirm
> > the property names are good enough? It's nice if Marc can help to
> > confirm before I'm going to work on next revision.
> >
> >      "highmem-ecam":    "on"/"off" on vms->highmem_ecam
> >      "highmem-mmio":    "on"/"off" on vms->highmem_mmio
> >      "highmem-redists": "on"/"off" on vms->highmem_redists
>
> I think that'd be reasonable, and would give the user some actual
> control over what gets exposed in the highmem region.
>
> I guess that the annoying thing with these options is that they allow
> the user to request conflicting settings (256 CPUs and
> highmem-redists=off, for example). You'll need to make this fail more
> or less gracefully.

Thanks for the quick confirm. The check is already existing in machvirt_init().
I think what we need is simply to calculate 'virt_max_cpus' with consideration
to 'highmem-redists' property there.

    if (max_cpus > virt_max_cpus) {
        error_report("Number of SMP CPUs requested (%d) exceeds max CPUs "
                     "supported by machine 'mach-virt' (%d)",
                     max_cpus, virt_max_cpus);
        exit(1);
    }

Thanks,
Gavin