Re: [Qemu-devel] [PATCH for-3.0 v2] pc: acpi: fix memory hotplug regression by reducing stub SRAT entry size

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 30 Jul 2018 17:26:24 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Mon, Jul 30, 2018 at 11:41:41AM +0200, Igor Mammedov wrote:
> > Commit 848a1cc1e (hw/acpi-build: build SRAT memory affinity structures for DIMM devices)
> > broke the first dimm hotplug in following cases:
> > 
> >  1: there is no coldplugged dimm in the last numa node
> >     but there is a coldplugged dimm in another node
> > 
> >   -m 4096,slots=4,maxmem=32G               \
> >   -object memory-backend-ram,id=m0,size=2G \
> >   -device pc-dimm,memdev=m0,node=0         \
> >   -numa node,nodeid=0                      \
> >   -numa node,nodeid=1
> > 
> >  2: if order of dimms on CLI is:
> >        1st plugged dimm in node1
> >        2nd plugged dimm in node0
> > 
> >   -m 4096,slots=4,maxmem=32G               \
> >   -object memory-backend-ram,size=2G,id=m0 \
> >   -device pc-dimm,memdev=m0,node=1         \
> >   -object memory-backend-ram,id=m1,size=2G \
> >   -device pc-dimm,memdev=m1,node=0         \
> >   -numa node,nodeid=0                      \
> >   -numa node,nodeid=1
> > 
> > (qemu) object_add memory-backend-ram,id=m2,size=1G
> > (qemu) device_add pc-dimm,memdev=m2,node=0
> > 
> > the first DIMM hotplug to any node except the last one
> > fails (Windows is unable to online it).
> > 
> > Length reduction of stub hotplug memory SRAT entry,
> > fixes issue for some reason.
> >   
> 
> I'm really bothered by the lack of automated testing for all
> these NUMA/ACPI corner cases.
> 
> This looks like a good candidate for an avocado_qemu test case.
> Can you show pseudo-code of how exactly the bug fix could be
> verified, so we can try to write a test case?
Sadly I do it manually every time I'm suspect a patch would
affect the feature. On just has to check if a new memory device
appeared in device manager and it is in working state (started successfully).
One also need to run it against to test it against windows version
that supports memory hot-add (DC ed.).

It's typically what RHEL QE does, and they just found
a new case which wasn't on test list so proactive measures
wouldn't work here in any case as we didn't know about
this particular combination.

I'm not sure how it will work with upstream avocado though,
windows testing implies tester would need access to MSDN
subscription or multiple retail versions to test against.
So with windows it becomes expensive and complicated
hence I'd leave this job to QE which has resources and
upstream would benefit from downstream when a bug is found
(albeit it's a catch up game).

> > RHBZ: 1609234  
> 
> I suggest including full URL of bug report[1].  I doubt anybody
> outside Red Hat knows what "RHBZ" means.
> 
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1609234
Next time I'll do so

> 
> > 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > ---
> > NOTE TO MAINTAINER: UPDATE REFERENCE APCI TABLE BLOBS
> > 
> > v2:
> >  fixup examples in commit message
> >  (they were in wrong order and with duplicate memdev=m1)
> > ---
> >  hw/i386/acpi-build.c | 19 ++++++++++---------
> >  1 file changed, 10 insertions(+), 9 deletions(-)
> > 
> > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > index 9e8350c..b52fdb2 100644
> > --- a/hw/i386/acpi-build.c
> > +++ b/hw/i386/acpi-build.c
> > @@ -2269,7 +2269,16 @@ static void build_srat_hotpluggable_memory(GArray *table_data, uint64_t base,
> >          numamem = acpi_data_push(table_data, sizeof *numamem);
> >  
> >          if (!info) {
> > -            build_srat_memory(numamem, cur, end - cur, default_node,
> > +            /*
> > +             * Entry is required for Windows to enable memory hotplug in OS
> > +             * and for Linux to enable SWIOTLB when booted with less than
> > +             * 4G of RAM. Windows works better if the entry sets proximity
> > +             * to the highest NUMA node in the machine at the end of the
> > +             * reserved space.
> > +             * Memory devices may override proximity set by this entry,
> > +             * providing _PXM method if necessary.
> > +             */
> > +            build_srat_memory(numamem, end - 1, 1, default_node,
> >                                MEM_AFFINITY_HOTPLUGGABLE | MEM_AFFINITY_ENABLED);
> >              break;
> >          }
> > @@ -2402,14 +2411,6 @@ build_srat(GArray *table_data, BIOSLinker *linker, MachineState *machine)
> >          build_srat_memory(numamem, 0, 0, 0, MEM_AFFINITY_NOFLAGS);
> >      }
> >  
> > -    /*
> > -     * Entry is required for Windows to enable memory hotplug in OS
> > -     * and for Linux to enable SWIOTLB when booted with less than
> > -     * 4G of RAM. Windows works better if the entry sets proximity
> > -     * to the highest NUMA node in the machine.
> > -     * Memory devices may override proximity set by this entry,
> > -     * providing _PXM method if necessary.
> > -     */
> >      if (hotplugabble_address_space_size) {
> >          build_srat_hotpluggable_memory(table_data, machine->device_memory->base,
> >                                         hotplugabble_address_space_size,
> > -- 
> > 2.7.4
> >   
>