Re: [Qemu-devel] [PATCH] x86/acpi: build SRAT when memory hotplug is enabled

[Dou Liyang]

Hi Eduardo, Thadeu,

At 09/02/2017 12:11 AM, Eduardo Habkost wrote:
> On Fri, Sep 01, 2017 at 12:45:42PM -0300, Thadeu Lima de Souza Cascardo wrote:
> > Linux uses SRAT to determine the maximum memory in a system, which is
> > used to determine whether to use the swiotlb for IOMMU or not for a
> > device that supports only 32 bits of addresses.
>
> Do you have a pointer to the corresponding Linux code, for
> reference?  Which SRAT entries Linux uses to make this decision?
>
> > When there is no NUMA configuration, qemu will not build SRAT. And when
> > memory hotplug is done, some Linux device drivers start failing.
> >
> > Tested by running with -m 512M,slots=8,maxmem=1G, adding the memory,
> > putting that online and using the system. Without the patch, swiotlb is
> > not used and ATA driver fails. With the patch, swiotlb is used, no
> > driver failure is observed.
> >
> > Signed-off-by: Thadeu Lima de Souza Cascardo <address@hidden>
>
> As far as I can see, this will only add APIC entries and a memory
> affinity entry for the first 640KB (which would be obviously
> wrong) if pcms->numa_nodes is 0.

In my opinion, this may also add the hotpluggable memory, and see the 
following commemts.

    /*
     * 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) {
        numamem = acpi_data_push(table_data, sizeof *numamem);
        build_srat_memory(numamem, pcms->hotplug_memory.base,
                          hotplugabble_address_space_size, 
pcms->numa_nodes - 1,
                          MEM_AFFINITY_HOTPLUGGABLE | 
MEM_AFFINITY_ENABLED);
    }


Thanks,
        dou.

> Once we apply the "Fix SRAT memory building in case of node 0
> without RAM" patch from Dou Liyang, no memory affinity entries
> will be generated if pcms->numa_nodes is 0.  Would this cause the
> problem to happen again?



> > ---
> >  hw/i386/acpi-build.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> > index 98dd424678..fb94249779 100644
> > --- a/hw/i386/acpi-build.c
> > +++ b/hw/i386/acpi-build.c
> > @@ -2645,6 +2645,9 @@ void acpi_build(AcpiBuildTables *tables, MachineState 
> > *machine)
> >      GArray *tables_blob = tables->table_data;
> >      AcpiSlicOem slic_oem = { .id = NULL, .table_id = NULL };
> >      Object *vmgenid_dev;
> > +    ram_addr_t hotplugabble_address_space_size =
> > +        object_property_get_int(OBJECT(pcms), PC_MACHINE_MEMHP_REGION_SIZE,
> > +                                NULL);
> >
> >      acpi_get_pm_info(&pm);
> >      acpi_get_misc_info(&misc);
> > @@ -2708,7 +2711,7 @@ void acpi_build(AcpiBuildTables *tables, MachineState 
> > *machine)
> >              build_tpm2(tables_blob, tables->linker);
> >          }
> >      }
> > -    if (pcms->numa_nodes) {
> > +    if (pcms->numa_nodes || hotplugabble_address_space_size) {
> >          acpi_add_table(table_offsets, tables_blob);
> >          build_srat(tables_blob, tables->linker, machine);
> >          if (have_numa_distance) {
> > --
> > 2.11.0