Re: [Qemu-devel] [PATCH] acpi: SRAT: do not create reserved gap entries

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 10 Aug 2018 16:06:57 +0200
Igor Mammedov <imammedo@redhat.com> wrote:

> Commit 848a1cc1e8b04 while introducing SRAT entries for DIMM and NVDIMM
> also introduced fake entries for gaps between memory devices, assuming
> that we need all possible range covered with SRAT entries.
> And it did it wrong since gap would overlap with preceeding entry.
> Reproduced with following CLI:
> 
>  -m 1G,slots=4,maxmem=8 \
>  -object memory-backend-ram,size=1G,id=m0 \
>  -device pc-dimm,memdev=m0,addr=0x101000000 \
>  -object memory-backend-ram,size=1G,id=m1 \
>  -device pc-dimm,memdev=m1
> 
> However recent development (10efd7e108) showed that gap entries might
> be not need. And indeed testing with WS2008DC-WS2016DC guests range
> shows that memory hotplug works just fine without gap entries.
> 
> So rather than fixing gap entry borders, just drop them altogether
> and simplify code around it.
> 
> Spotted-by: Laszlo Ersek <lersek@redhat.com>
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
> There is no need to update reference blobs since gaps beween dimms
> aren't generated by any exsting test case.
> 
> Considering issue is not visible by default lets just merge it into 3.1
> and stable 3.0.1
Pls ignore it for now I'll need to do more extensive testing with old kernels,
we might need these holes for old kernels or even new ones.
/me goes to read kernel code

/per spec possible to hotplug range could be in SRAT,
 even though I don't like it bu we might end up with static
 partitioning of hotplug area between nodes like on bare metal
 to avoid chasing after unknown requirements from windows /


> ---
>  hw/i386/acpi-build.c | 62 +++++++++++++++++++---------------------------------
>  1 file changed, 22 insertions(+), 40 deletions(-)
> 
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index e1ee8ae..d3d690f 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -2254,48 +2254,16 @@ build_tpm2(GArray *table_data, BIOSLinker *linker, GArray *tcpalog)
>  static void build_srat_hotpluggable_memory(GArray *table_data, uint64_t base,
>                                             uint64_t len, int default_node)
>  {
> -    MemoryDeviceInfoList *info_list = qmp_memory_device_list();
>      MemoryDeviceInfoList *info;
> -    MemoryDeviceInfo *mi;
> -    PCDIMMDeviceInfo *di;
> -    uint64_t end = base + len, cur, size;
> -    bool is_nvdimm;
>      AcpiSratMemoryAffinity *numamem;
> -    MemoryAffinityFlags flags;
> +    MemoryDeviceInfoList *info_list = qmp_memory_device_list();;
>  
> -    for (cur = base, info = info_list;
> -         cur < end;
> -         cur += size, info = info->next) {
> -        numamem = acpi_data_push(table_data, sizeof *numamem);
> -
> -        if (!info) {
> -            /*
> -             * 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;
> -        }
> -
> -        mi = info->value;
> -        is_nvdimm = (mi->type == MEMORY_DEVICE_INFO_KIND_NVDIMM);
> -        di = !is_nvdimm ? mi->u.dimm.data : mi->u.nvdimm.data;
> -
> -        if (cur < di->addr) {
> -            build_srat_memory(numamem, cur, di->addr - cur, default_node,
> -                              MEM_AFFINITY_HOTPLUGGABLE | MEM_AFFINITY_ENABLED);
> -            numamem = acpi_data_push(table_data, sizeof *numamem);
> -        }
> -
> -        size = di->size;
> +    for (info = info_list; info != NULL; info = info->next) {
> +        MemoryAffinityFlags flags = MEM_AFFINITY_ENABLED;
> +        MemoryDeviceInfo *mi = info->value;
> +        bool is_nvdimm = (mi->type == MEMORY_DEVICE_INFO_KIND_NVDIMM);
> +        PCDIMMDeviceInfo *di = !is_nvdimm ? mi->u.dimm.data : mi->u.nvdimm.data;
>  
> -        flags = MEM_AFFINITY_ENABLED;
>          if (di->hotpluggable) {
>              flags |= MEM_AFFINITY_HOTPLUGGABLE;
>          }
> @@ -2303,10 +2271,24 @@ static void build_srat_hotpluggable_memory(GArray *table_data, uint64_t base,
>              flags |= MEM_AFFINITY_NON_VOLATILE;
>          }
>  
> -        build_srat_memory(numamem, di->addr, size, di->node, flags);
> +        numamem = acpi_data_push(table_data, sizeof *numamem);
> +        build_srat_memory(numamem, di->addr, di->size, di->node, flags);
>      }
> -
>      qapi_free_MemoryDeviceInfoList(info_list);
> +
> +    /*
> +     * 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.
> +     */
> +    numamem = acpi_data_push(table_data, sizeof *numamem);
> +    build_srat_memory(numamem, base + len - 1, 1, default_node,
> +                      MEM_AFFINITY_HOTPLUGGABLE | MEM_AFFINITY_ENABLED);
> +
>  }
>  
>  static void