Introduce the `cpus` property, named as such for dom0less compatibility, that
represents the maximum number of vpcus to allocate for a domain. In the device
tree, it will be encoded as a u32 value.

Signed-off-by: Daniel P. Smith <dpsmith@apertussolutions.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>
---
Changes since v1:
- switched from match_fdt to strncmp
- switched to nested else if
- dropped ternary for name selection
---
 xen/arch/x86/dom0_build.c             |  3 +++
 xen/arch/x86/domain-builder/fdt.c     | 11 +++++++++++
 xen/arch/x86/include/asm/bootdomain.h |  2 ++
 3 files changed, 16 insertions(+)

diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
index 1c3b7ff0e658..7ff052016bfd 100644
--- a/xen/arch/x86/dom0_build.c
+++ b/xen/arch/x86/dom0_build.c
@@ -617,6 +617,9 @@ int __init construct_dom0(struct boot_domain *bd)
     if ( !get_memsize(&dom0_max_size, LONG_MAX) && bd->max_pages )
         dom0_size.nr_pages = bd->max_pages;
 
+    if ( opt_dom0_max_vcpus_max == UINT_MAX && bd->max_vcpus )
+        opt_dom0_max_vcpus_max = bd->max_vcpus;
+
     if ( is_hvm_domain(d) )
         rc = dom0_construct_pvh(bd);
     else if ( is_pv_domain(d) )
diff --git a/xen/arch/x86/domain-builder/fdt.c b/xen/arch/x86/domain-builder/fdt.c
index aff1b8c3235d..70a793db199b 100644
--- a/xen/arch/x86/domain-builder/fdt.c
+++ b/xen/arch/x86/domain-builder/fdt.c
@@ -147,6 +147,17 @@ static int __init process_domain_node(
             bd->max_pages = PFN_DOWN(kb * SZ_1K);
             printk("  max memory: %ld kb\n", kb);
         }
+        else if ( strncmp(prop_name, "cpus", name_len) == 0 )
+        {
+            uint32_t val = UINT_MAX;
+            if ( fdt_prop_as_u32(prop, &val) != 0 )
+            {
+                printk("  failed processing max_vcpus for domain %s\n", name);
+                return -EINVAL;
+            }
+            bd->max_vcpus = val;
+            printk("  max vcpus: %d\n", bd->max_vcpus);
+        }
     }
 
     fdt_for_each_subnode(node, fdt, dom_node)
diff --git a/xen/arch/x86/include/asm/bootdomain.h b/xen/arch/x86/include/asm/bootdomain.h
index d7092bc32ad7..1a15273043f5 100644
--- a/xen/arch/x86/include/asm/bootdomain.h
+++ b/xen/arch/x86/include/asm/bootdomain.h
@@ -24,6 +24,8 @@ struct boot_domain {
     unsigned long min_pages;
     unsigned long max_pages;
 
+    unsigned int max_vcpus;
+
     struct boot_module *kernel;
     struct boot_module *ramdisk;
 
-- 
2.30.2

On 26.12.2024 17:57, Daniel P. Smith wrote:
> --- a/xen/arch/x86/domain-builder/fdt.c
> +++ b/xen/arch/x86/domain-builder/fdt.c
> @@ -147,6 +147,17 @@ static int __init process_domain_node(
>              bd->max_pages = PFN_DOWN(kb * SZ_1K);
>              printk("  max memory: %ld kb\n", kb);
>          }
> +        else if ( strncmp(prop_name, "cpus", name_len) == 0 )
> +        {
> +            uint32_t val = UINT_MAX;

It's not the first time I see such an initializer, yet it's even more
pronounced here, as the call ...

> +            if ( fdt_prop_as_u32(prop, &val) != 0 )

... is coming right next. If that function succeeds, it surely should
set its output? And if it didn't, you're as hosed with initializer as
you're without.

Jan

On 2024-12-26 11:57, Daniel P. Smith wrote:
> Introduce the `cpus` property, named as such for dom0less compatibility, that
> represents the maximum number of vpcus to allocate for a domain. In the device
> tree, it will be encoded as a u32 value.

s/vpcus/vcpus/

I would remove "maximum".  Today, the DT only has `cpus`, and you get 
all of them.  So implicitly cpus=max_vcpus.

I could see a future max_vcpus property.  In that case, you would get 
`cpus` online and the rest offline.

> Signed-off-by: Daniel P. Smith <dpsmith@apertussolutions.com>
> Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>

> diff --git a/xen/arch/x86/domain-builder/fdt.c b/xen/arch/x86/domain-builder/fdt.c
> index aff1b8c3235d..70a793db199b 100644
> --- a/xen/arch/x86/domain-builder/fdt.c
> +++ b/xen/arch/x86/domain-builder/fdt.c
> @@ -147,6 +147,17 @@ static int __init process_domain_node(
>               bd->max_pages = PFN_DOWN(kb * SZ_1K);
>               printk("  max memory: %ld kb\n", kb);
>           }
> +        else if ( strncmp(prop_name, "cpus", name_len) == 0 )
> +        {
> +            uint32_t val = UINT_MAX;
> +            if ( fdt_prop_as_u32(prop, &val) != 0 )
> +            {
> +                printk("  failed processing max_vcpus for domain %s\n", name);

s/max_vcpus/cpus/

Regards,
Jason