Re: [PATCH 2/2] hw/acpi: i386: bump MADT to revision 5

[Igor Mammedov]

On Wed, 29 Mar 2023 08:16:26 -0500
Eric DeVolder <eric.devolder@oracle.com> wrote:

> On 3/29/23 00:03, Michael S. Tsirkin wrote:
> > On Tue, Mar 28, 2023 at 11:59:26AM -0400, Eric DeVolder wrote:  
> >> Currently i386 QEMU generates MADT revision 3, and reports
> >> MADT revision 1. ACPI 6.3 introduces MADT revision 5.
> >>
> >> For MADT revision 4, that introduces ARM GIC structures, which do
> >> not apply to i386.
> >>
> >> For MADT revision 5, the Local APIC flags introduces the Online
> >> Capable bitfield.
> >>
> >> Making MADT generate and report revision 5 will solve problems with
> >> CPU hotplug (the Online Capable flag indicates hotpluggable CPUs).
> >>
> >> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>  
> > 
> > I am looking for ways to reduce risk of breakage with this.
> > We don't currently have a reason to change it if cpu
> > hotplug is off, do we? Maybe make it conditional on that.  
> 
> By "cpu hotplug off", do you mean, for example, no maxcpus= option?
> In other words, how should I detect "cpu hotplug off"?
> eric
I'm not sure that it's possible disable CPU hotplug at all.
even if one doesn't have maxcpus on CLI present CPUs are described
as hotpluggbale and can be unplugged and re-plugged later.