On Fri, 1 Sep 2017 13:11:18 -0300 Eduardo Habkost <ehabk...@redhat.com> 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? ec941c5f x86/mm/64: Enable SWIOTLB if system has SRAT memory regions above MAX_DMA32_PFN > > 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. I think safest way to achieve what patch needs is to enable add numa node implicitly if user hasn't done it explicitly on CLI when memory hotplug is enabled i.e. slots != 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 > > >