If qemu is started with a proximity node containing CPUs alone,
it will provide one of these structures to say memory in this
node is directly connected to itself.

This description is arguably pointless even if there is memory
in the node.  If there is no memory present, and hence no SRAT
entry it breaks Linux HMAT passing and the table is rejected.

https://elixir.bootlin.com/linux/latest/source/drivers/acpi/numa/hmat.c#L444

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 hw/acpi/hmat.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hw/acpi/hmat.c b/hw/acpi/hmat.c
index 3042d223c8..723ae28d32 100644
--- a/hw/acpi/hmat.c
+++ b/hw/acpi/hmat.c
@@ -204,6 +204,13 @@ static void hmat_build_table_structs(GArray *table_data, NumaState *numa_state)
     build_append_int_noprefix(table_data, 0, 4); /* Reserved */
 
     for (i = 0; i < numa_state->num_nodes; i++) {
+        /*
+         * Linux rejects whole HMAT table if a node with no memory
+         * has one of these structures listing it as a target.
+         */
+        if (!numa_state->nodes[i].node_mem) {
+            continue;
+        }
         flags = 0;
 
         if (numa_state->nodes[i].initiator < MAX_NODES) {
-- 
2.39.2

On Thu, Feb 29, 2024 at 04:25:44PM +0000, Jonathan Cameron wrote:
> If qemu is started with a proximity node containing CPUs alone,
> it will provide one of these structures to say memory in this
> node is directly connected to itself.
> 
> This description is arguably pointless even if there is memory
> in the node.  If there is no memory present, and hence no SRAT
> entry it breaks Linux HMAT passing and the table is rejected.
> 
> https://elixir.bootlin.com/linux/latest/source/drivers/acpi/numa/hmat.c#L444
> 

Nit: This link becomes out of date pretty much immediately, consider
using a versioned link.

> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
>  hw/acpi/hmat.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/hw/acpi/hmat.c b/hw/acpi/hmat.c
> index 3042d223c8..723ae28d32 100644
> --- a/hw/acpi/hmat.c
> +++ b/hw/acpi/hmat.c
> @@ -204,6 +204,13 @@ static void hmat_build_table_structs(GArray *table_data, NumaState *numa_state)
>      build_append_int_noprefix(table_data, 0, 4); /* Reserved */
>  
>      for (i = 0; i < numa_state->num_nodes; i++) {
> +        /*
> +         * Linux rejects whole HMAT table if a node with no memory
> +         * has one of these structures listing it as a target.
> +         */
> +        if (!numa_state->nodes[i].node_mem) {
> +            continue;
> +        }
>          flags = 0;
>  
>          if (numa_state->nodes[i].initiator < MAX_NODES) {
> -- 
> 2.39.2
> 
>

On Thu, 29 Feb 2024 12:28:51 -0500
Gregory Price <gregory.price@memverge.com> wrote:

> On Thu, Feb 29, 2024 at 04:25:44PM +0000, Jonathan Cameron wrote:
> > If qemu is started with a proximity node containing CPUs alone,
> > it will provide one of these structures to say memory in this
> > node is directly connected to itself.
> > 
> > This description is arguably pointless even if there is memory
> > in the node.  If there is no memory present, and hence no SRAT
> > entry it breaks Linux HMAT passing and the table is rejected.
> > 
> > https://elixir.bootlin.com/linux/latest/source/drivers/acpi/numa/hmat.c#L444
> >   
> 
> Nit: This link becomes out of date pretty much immediately, consider
> using a versioned link.
Good point.

https://elixir.bootlin.com/linux/v6.7/source/drivers/acpi/numa/hmat.c#L444

> 
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > ---
> >  hw/acpi/hmat.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/hw/acpi/hmat.c b/hw/acpi/hmat.c
> > index 3042d223c8..723ae28d32 100644
> > --- a/hw/acpi/hmat.c
> > +++ b/hw/acpi/hmat.c
> > @@ -204,6 +204,13 @@ static void hmat_build_table_structs(GArray *table_data, NumaState *numa_state)
> >      build_append_int_noprefix(table_data, 0, 4); /* Reserved */
> >  
> >      for (i = 0; i < numa_state->num_nodes; i++) {
> > +        /*
> > +         * Linux rejects whole HMAT table if a node with no memory
> > +         * has one of these structures listing it as a target.
> > +         */
> > +        if (!numa_state->nodes[i].node_mem) {
> > +            continue;
> > +        }
> >          flags = 0;
> >  
> >          if (numa_state->nodes[i].initiator < MAX_NODES) {
> > -- 
> > 2.39.2
> > 
> >