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 <casca...@canonical.com>
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.
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
>
--
Eduardo
