Re: [Qemu-devel] [PATCH v5 1/3] hw/acpi-build: Fix SRAT memory building in case of node 0 without RAM

[Eduardo Habkost <ehabkost@redhat.com>]

On Thu, Aug 31, 2017 at 08:04:26PM +0800, Dou Liyang wrote:
> From: Eduardo Habkost <ehabkost@redhat.com>
> 
> Currently, Using the fisrt node without memory on the machine makes
> QEMU unhappy. With this example command line:
>   ... \
>   -m 1024M,slots=4,maxmem=32G \
>   -numa node,nodeid=0 \
>   -numa node,mem=1024M,nodeid=1 \
>   -numa node,nodeid=2 \
>   -numa node,nodeid=3 \
> Guest reports "No NUMA configuration found" and the NUMA topology is
> wrong.
> 
> This is because when QEMU builds ACPI SRAT, it regards node 0 as the
> default node to deal with the memory hole(640K-1M). this means the
> node0 must have some memory(>1M), but, actually it can have no
> memory.
> 
> Fix this problem by  cut out the 640K hole in the same way the PCI
> 4G hole does. Also do some cleanup.
> 
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
> ---
>  hw/i386/acpi-build.c | 30 +++++++++++++++++++++++-------
>  1 file changed, 23 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index 98dd424..48525a1 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -2318,6 +2318,9 @@ build_tpm2(GArray *table_data, BIOSLinker *linker)
>                   (void *)tpm2_ptr, "TPM2", sizeof(*tpm2_ptr), 4, NULL, NULL);
>  }
>  
> +#define HOLE_640K_START  (640 * 1024)
> +#define HOLE_640K_END   (1024 * 1024)
> +
>  static void
>  build_srat(GArray *table_data, BIOSLinker *linker, MachineState *machine)
>  {
> @@ -2373,17 +2376,30 @@ build_srat(GArray *table_data, BIOSLinker *linker, MachineState *machine)
>      next_base = 0;
>      numa_start = table_data->len;
>  
> -    numamem = acpi_data_push(table_data, sizeof *numamem);
> -    build_srat_memory(numamem, 0, 640 * 1024, 0, MEM_AFFINITY_ENABLED);
> -    next_base = 1024 * 1024;
>      for (i = 1; i < pcms->numa_nodes + 1; ++i) {
>          mem_base = next_base;
>          mem_len = pcms->node_mem[i - 1];
> -        if (i == 1) {
> -            mem_len -= 1024 * 1024;
> -        }
>          next_base = mem_base + mem_len;
>  
> +        /* Cut out the 640K hole */
> +        if (mem_base <= HOLE_640K_START &&
> +            next_base > HOLE_640K_START) {
> +            mem_len -= next_base - HOLE_640K_START;
> +            if (mem_len > 0) {
> +                numamem = acpi_data_push(table_data, sizeof *numamem);
> +                build_srat_memory(numamem, mem_base, mem_len, i - 1,
> +                                  MEM_AFFINITY_ENABLED);
> +            }
> +
> +            /* Check for the rare case: 640K < RAM < 1M */
> +            if (next_base <= HOLE_640K_END) {
> +                next_base = HOLE_640K_END;
> +                continue;
> +            }
> +            mem_base = HOLE_640K_END;
> +            mem_len = next_base - HOLE_640K_END;
> +        }
> +
>          /* Cut out the ACPI_PCI hole */
>          if (mem_base <= pcms->below_4g_mem_size &&
>              next_base > pcms->below_4g_mem_size) {
> @@ -2395,7 +2411,7 @@ build_srat(GArray *table_data, BIOSLinker *linker, MachineState *machine)
>              }
>              mem_base = 1ULL << 32;
>              mem_len = next_base - pcms->below_4g_mem_size;
> -            next_base += (1ULL << 32) - pcms->below_4g_mem_size;
> +            next_base = mem_base + mem_len;

Is this extra change intentional?

I find the code more readable with it, but it should go in a
separate patch because it is unrelated to the bug fix.

-- 
Eduardo